feat: serverless 2.0.0 architecture with Authentik auth proxy

Implements a complete serverless development container platform:

## Architecture
- Authentik forward auth for authentication/authorization
- NGINX routing proxy extracts GitHub repo from URL path
- Knative Service auto-scales dev container instances from 0
- Dynamic GitHub repo routing via /github/{owner}/{repo}

## Components
- routing-proxy: NGINX-based service for repo extraction and forwarding
- deployment.yaml: Complete K8s manifests (proxy, Knative, ingress, secrets)
- authentik-config.yaml: Authentik application and provider configs
- serverless scripts: Dynamic repo initialization and startup handling
- Comprehensive documentation and Makefile for ops

## Key Features
- Scale to zero when not in use (cost-effective)
- Per-request isolation (each repo gets own container)
- Built-in file manager for upload/download
- Support for private repos via GitHub tokens
- User attribution via Authentik headers
- WebSocket support for VNC connections

Example usage: https://devcontainer.farh.net/github/microsoft/vscode

Generated with [Claude Code](https://claude.ai/code)
via [Happy](https://happy.engineering)

Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

serverless/scripts/serverless-startapp.sh

@@ -0,0 +1,86 @@
+#!/bin/bash
+
+# Serverless-aware startup script for devcontainer
+# This replaces the standard /startapp.sh when in serverless mode
+
+set -e
+
+log() {
+    echo "[$(date '+%Y-%m-%d %H:%M:%S')] SERVERLESS-START: $*" >&2
+}
+
+log "Starting serverless devcontainer..."
+log "Mode: ${SERVERLESS_MODE:-traditional}"
+log "IDE: ${IDE:-vscode}"
+
+# Wait for HTTP headers to be available (in case of init container pattern)
+# In Knative, the headers should be available immediately as env vars
+sleep 2
+
+# Check if we're in serverless mode with dynamic routing
+if [[ "$SERVERLESS_MODE" == "true" && "$DYNAMIC_GITHUB_ROUTING" == "true" ]]; then
+    log "Dynamic GitHub routing enabled"
+
+    # In Knative, HTTP headers become environment variables with HTTP_ prefix
+    # But we also check for the unprefixed versions set by proxies
+    AVAILABLE_VARS=$(env | grep -E "(GITHUB|AUTHENTIK|X_)" | sort)
+    if [[ -n "$AVAILABLE_VARS" ]]; then
+        log "Available routing variables:"
+        echo "$AVAILABLE_VARS" | while read -r var; do
+            log "  $var"
+        done
+    else
+        log "No routing variables found, checking for alternatives..."
+        # Check if there's a file with the repo info
+        if [[ -f "/tmp/github-repo" ]]; then
+            export GITHUB_REPO=$(cat /tmp/github-repo)
+            log "Found repo file: $GITHUB_REPO"
+        else
+            log "ERROR: No GitHub repository information available"
+            log "Expected routing headers or /tmp/github-repo file"
+            exit 1
+        fi
+    fi
+
+    # Use the dynamic initialization script
+    source /usr/local/bin/dynamic-init-repo
+else
+    log "Using standard initialization..."
+    # Use the standard initialization
+    source /usr/local/bin/init-repo
+fi
+
+# At this point, WORKSPACE_DIR should be set by the init script
+WORKSPACE_DIR="${WORKSPACE_DIR:-/workspace}"
+log "Working directory: $WORKSPACE_DIR"
+
+# Ensure we're in the workspace directory
+cd "$WORKSPACE_DIR"
+
+# Launch the appropriate IDE based on the IDE environment variable
+case "${IDE:-vscode}" in
+    "vscode")
+        log "Starting VSCode..."
+        exec code --new-window --wait "$WORKSPACE_DIR"
+        ;;
+    "antigravity")
+        log "Starting Antigravity..."
+        exec antigravity \
+            --no-sandbox \
+            --user-data-dir ~/.config/antigravity \
+            --disable-dev-shm-usage \
+            --disable-gpu \
+            --disable-features=VizDisplayCompositor \
+            --new-window \
+            "$WORKSPACE_DIR"
+        ;;
+    "none")
+        log "No IDE requested, keeping container alive..."
+        exec sleep infinity
+        ;;
+    *)
+        log "ERROR: Unknown IDE type: $IDE"
+        log "Valid options: vscode, antigravity, none"
+        exit 1
+        ;;
+esac