fix(backend): P2 config & Docker consistency

Resolve the operational/config sprawl (#10-#14 from the review): the app read
NORMOGEN_*/MONGODB_* env vars but every env/compose file set SERVER_*/DATABASE_*,
the ports were all over the place (8080/8000/6500/6800), there were 5
inconsistent Dockerfiles (rust:1.82 vs rust:1.93, missing curl), and an 18 MB
binary was committed.

Env-var names — standardize on what the code reads:
* config/mod.rs: NORMOGEN_PORT default 8080 -> 6500 (avoid the over-common
  8000/8080).
* db/mod.rs: create_database() now reads MONGODB_DATABASE (was DATABASE_NAME).
* .env.example, defaults.env, docker-compose.yml, docker-compose.dev.yml,
  DEPLOYMENT_GUIDE.md, deployment/README.md, deploy-and-test-solaria.sh,
  deploy-local-build.sh: use NORMOGEN_HOST/NORMOGEN_PORT/MONGODB_URI/
  MONGODB_DATABASE/APP_ENVIRONMENT; drop the dead SERVER_*/DATABASE_URI/
  DATABASE_NAME names.

Ports — canonical container port 6500 everywhere:
* Both Dockerfiles EXPOSE 6500; prod compose maps 6500:6500, dev 6501:6500.
* Bulk-replaced the long tail of solaria:8000/localhost:8000/localhost:8080 in
  docs and test scripts -> 6500.

Dockerfiles — 2 canonical, rust:latest, curl + healthcheck:
* backend/Dockerfile (prod): rust:latest builder, debian runtime now installs
  curl (so the compose HEALTHCHECK actually works), EXPOSE 6500.
* backend/docker/Dockerfile.dev (dev): rust:latest both stages, EXPOSE 6500.
* Deleted 3 redundant Dockerfiles (Dockerfile.improved x2, docker/Dockerfile).
* Deleted the committed 18 MB binary backend/docker/normogen-backend.
* Deleted 2 stray fix-notes in backend/docker/.

Compose:
* docker-compose.yml: correct env names, 6500:6500, APP_ENVIRONMENT=production,
  JWT_SECRET/ENCRYPTION_KEY required via compose interpolation, dropped the
  obsolete top-level version: key.
* docker-compose.dev.yml: correct env names, 6501:6500, mongo:7 (was 6.0),
  added a working backend healthcheck.
* Deleted docker/docker-compose.improved.yml + backend/deploy-to-solaria-improved.sh
  (built around the now-deleted 'improved' Docker files).

Verified: cargo fmt --check clean, build + clippy --all-targets clean, 18 unit
tests pass; grep confirms no SERVER_*/DATABASE_* env names and no rust:1.x tags
remain outside docs/archive and docs/adr (historical).

docs/deployment/DEPLOYMENT_GUIDE.md

@@ -83,19 +83,19 @@ docker-compose logs -f backend
 
 ### Base URL
 ```
-http://solaria:8000
+http://solaria:6500
 ```
 
 ### Public Endpoints (No Auth)
 
 #### Health Check
 ```bash
-curl http://solaria:8000/health
+curl http://solaria:6500/health
 ```
 
 #### Register
 ```bash
-curl -X POST http://solaria:8000/api/auth/register \
+curl -X POST http://solaria:6500/api/auth/register \
   -H "Content-Type: application/json" \
   -d '{
     "email": "test@example.com",
@@ -106,7 +106,7 @@ curl -X POST http://solaria:8000/api/auth/register \
 
 #### Login
 ```bash
-curl -X POST http://solaria:8000/api/auth/login \
+curl -X POST http://solaria:6500/api/auth/login \
   -H "Content-Type: application/json" \
   -d '{
     "email": "test@example.com",
@@ -116,7 +116,7 @@ curl -X POST http://solaria:8000/api/auth/login \
 
 #### Set Recovery Phrase
 ```bash
-curl -X POST http://solaria:8000/api/auth/set-recovery-phrase \
+curl -X POST http://solaria:6500/api/auth/set-recovery-phrase \
   -H "Content-Type: application/json" \
   -d '{
     "email": "test@example.com",
@@ -126,7 +126,7 @@ curl -X POST http://solaria:8000/api/auth/set-recovery-phrase \
 
 #### Recover Password
 ```bash
-curl -X POST http://solaria:8000/api/auth/recover-password \
+curl -X POST http://solaria:6500/api/auth/recover-password \
   -H "Content-Type: application/json" \
   -d '{
     "email": "test@example.com",
@@ -139,13 +139,13 @@ curl -X POST http://solaria:8000/api/auth/recover-password \
 
 #### Get Profile
 ```bash
-curl http://solaria:8000/api/users/me \
+curl http://solaria:6500/api/users/me \
   -H "Authorization: Bearer YOUR_ACCESS_TOKEN"
 ```
 
 #### Update Profile
 ```bash
-curl -X PUT http://solaria:8000/api/users/me \
+curl -X PUT http://solaria:6500/api/users/me \
   -H "Content-Type: application/json" \
   -H "Authorization: Bearer YOUR_ACCESS_TOKEN" \
   -d '{
@@ -155,13 +155,13 @@ curl -X PUT http://solaria:8000/api/users/me \
 
 #### Get Settings
 ```bash
-curl http://solaria:8000/api/users/me/settings \
+curl http://solaria:6500/api/users/me/settings \
   -H "Authorization: Bearer YOUR_ACCESS_TOKEN"
 ```
 
 #### Update Settings
 ```bash
-curl -X PUT http://solaria:8000/api/users/me/settings \
+curl -X PUT http://solaria:6500/api/users/me/settings \
   -H "Content-Type: application/json" \
   -H "Authorization: Bearer YOUR_ACCESS_TOKEN" \
   -d '{
@@ -171,7 +171,7 @@ curl -X PUT http://solaria:8000/api/users/me/settings \
 
 #### Change Password
 ```bash
-curl -X POST http://solaria:8000/api/users/me/change-password \
+curl -X POST http://solaria:6500/api/users/me/change-password \
   -H "Content-Type: application/json" \
   -H "Authorization: Bearer YOUR_ACCESS_TOKEN" \
   -d '{
@@ -182,7 +182,7 @@ curl -X POST http://solaria:8000/api/users/me/change-password \
 
 #### Delete Account
 ```bash
-curl -X DELETE http://solaria:8000/api/users/me \
+curl -X DELETE http://solaria:6500/api/users/me \
   -H "Authorization: Bearer YOUR_ACCESS_TOKEN" \
   -d '{
     "confirmation": "DELETE_ACCOUNT"
@@ -191,7 +191,7 @@ curl -X DELETE http://solaria:8000/api/users/me \
 
 #### Create Share
 ```bash
-curl -X POST http://solaria:8000/api/shares \
+curl -X POST http://solaria:6500/api/shares \
   -H "Content-Type: application/json" \
   -H "Authorization: Bearer YOUR_ACCESS_TOKEN" \
   -d '{
@@ -204,13 +204,13 @@ curl -X POST http://solaria:8000/api/shares \
 
 #### List Shares
 ```bash
-curl http://solaria:8000/api/shares \
+curl http://solaria:6500/api/shares \
   -H "Authorization: Bearer YOUR_ACCESS_TOKEN"
 ```
 
 #### Update Share
 ```bash
-curl -X PUT http://solaria:8000/api/shares/SHARE_ID \
+curl -X PUT http://solaria:6500/api/shares/SHARE_ID \
   -H "Content-Type: application/json" \
   -H "Authorization: Bearer YOUR_ACCESS_TOKEN" \
   -d '{
@@ -220,13 +220,13 @@ curl -X PUT http://solaria:8000/api/shares/SHARE_ID \
 
 #### Delete Share
 ```bash
-curl -X DELETE http://solaria:8000/api/shares/SHARE_ID \
+curl -X DELETE http://solaria:6500/api/shares/SHARE_ID \
   -H "Authorization: Bearer YOUR_ACCESS_TOKEN"
 ```
 
 #### Check Permission
 ```bash
-curl -X POST http://solaria:8000/api/permissions/check \
+curl -X POST http://solaria:6500/api/permissions/check \
   -H "Content-Type: application/json" \
   -H "Authorization: Bearer YOUR_ACCESS_TOKEN" \
   -d '{
@@ -237,19 +237,19 @@ curl -X POST http://solaria:8000/api/permissions/check \
 
 #### Get Sessions (NEW)
 ```bash
-curl http://solaria:8000/api/sessions \
+curl http://solaria:6500/api/sessions \
   -H "Authorization: Bearer YOUR_ACCESS_TOKEN"
 ```
 
 #### Revoke Session (NEW)
 ```bash
-curl -X DELETE http://solaria:8000/api/sessions/SESSION_ID \
+curl -X DELETE http://solaria:6500/api/sessions/SESSION_ID \
   -H "Authorization: Bearer YOUR_ACCESS_TOKEN"
 ```
 
 #### Revoke All Sessions (NEW)
 ```bash
-curl -X DELETE http://solaria:8000/api/sessions/all \
+curl -X DELETE http://solaria:6500/api/sessions/all \
   -H "Authorization: Bearer YOUR_ACCESS_TOKEN"
 ```
 
@@ -309,8 +309,9 @@ JWT_SECRET=your-super-secret-jwt-key-min-32-chars
 MONGODB_URI=mongodb://mongodb:27017
 MONGODB_DATABASE=normogen
 RUST_LOG=info
-SERVER_PORT=8000
-SERVER_HOST=0.0.0.0
+NORMOGEN_PORT=6500
+NORMOGEN_HOST=0.0.0.0
+APP_ENVIRONMENT=production
 ```
 
 ## Security Features (Phase 2.6)