chore: remove all NestJS backend references, replace with Hono/Bun

- Delete nestjs-backend.md guideline (replaced by hono-server.md)
- Delete Dockerfile.nestjs-base and Dockerfile.nestjs templates
- Delete stale BACKEND_ARCHITECTURE.md doc (NestJS-era, obsolete)
- Update CLAUDE.md, GUIDELINES.md, authentication.md to Hono/Bun first
- Update all app CLAUDE.md files: backend/ → server/, NestJS → Hono+Bun
- Update all app package.json files: @*/backend → @*/server
- Update docs: LOCAL_DEVELOPMENT, PORT_SCHEMA, ENVIRONMENT_VARIABLES,
  DATABASE_MIGRATIONS, MAC_MINI_SERVER, PROJECT_OVERVIEW
- Update scripts: generate-env.mjs, setup-databases.sh, build-app.sh
- Update CI/CD: cd-macmini.yml backend → server paths
- Update Astro docs site: @chat/backend → @chat/server

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.github/workflows/cd-macmini.yml

@@ -259,16 +259,6 @@ jobs:
           SERVICES="${{ steps.services.outputs.services }}"
           DEPLOY_ALL="${{ steps.services.outputs.deploy-all }}"
 
-          # Check if any backend service is being deployed
-          NEEDS_BASE=false
-          if [ "$DEPLOY_ALL" == "true" ]; then
-            NEEDS_BASE=true
-          else
-            for svc in $SERVICES; do
-              case "$svc" in *-backend) NEEDS_BASE=true; break ;; esac
-            done
-          fi
-
           NEEDS_WEB_BASE=false
           if [ "$DEPLOY_ALL" == "true" ]; then
             NEEDS_WEB_BASE=true
@@ -278,14 +268,6 @@ jobs:
             done
           fi
 
-          if [ "$NEEDS_BASE" == "true" ]; then
-            echo "=== Building shared NestJS base image ==="
-            docker build -f docker/Dockerfile.nestjs-base -t nestjs-base:local . 2>&1 | tail -5
-            echo "NestJS base image built"
-          else
-            echo "No backends to deploy, skipping NestJS base image"
-          fi
-
           if [ "$NEEDS_WEB_BASE" == "true" ]; then
             echo "=== Building shared SvelteKit base image ==="
             docker build -f docker/Dockerfile.sveltekit-base -t sveltekit-base:local . 2>&1 | tail -5