Add local development environment with switchable backend

Set up local dev workflow: SSH tunnel to dev DB, Next.js API proxy
via rewrites, Docker or native backend on port 5000. Update and
restructure project documentation.

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

scripts/local-backend-docker.ps1

@@ -0,0 +1,4 @@
+Write-Host "Starting Docker backend on http://localhost:5000" -ForegroundColor Cyan
+Write-Host "Requires: SSH tunnel running (scripts/local-tunnel.ps1)"
+Write-Host ""
+docker compose -f "$PSScriptRoot\..\deploy\docker-compose.local.yml" up --build

scripts/local-backend-dotnet.ps1

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+Write-Host "Starting backend (dotnet run) on http://localhost:5000" -ForegroundColor Cyan
+Write-Host "Requires: SSH tunnel running (scripts/local-tunnel.ps1)"
+Write-Host ""
+Push-Location "$PSScriptRoot\..\backend"
+dotnet run --project src/GBSite.Api
+Pop-Location

scripts/local-frontend.ps1

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+Write-Host "Starting frontend on http://localhost:3000" -ForegroundColor Cyan
+Write-Host "API proxy -> http://localhost:5000"
+Write-Host ""
+Push-Location "$PSScriptRoot\..\frontend"
+npm run dev
+Pop-Location

scripts/local-tunnel.ps1

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+Write-Host "SSH Tunnel: localhost:5433 -> server:5432 (dev_db)" -ForegroundColor Cyan
+Write-Host "Press Ctrl+C to stop"
+Write-Host ""
+ssh -N -L 5433:127.0.0.1:5432 -o ServerAliveInterval=60 deploy@31.131.18.254