Feat v0.8.1 workspace module

Managed disk directories for extensions needing real filesystem access
(git, compilers, media tools). Five builtins: create, path, list,
delete, usage. Extension-scoped to {WORKSPACE_ROOT}/{packageID}/{name}/.

- New sandbox/workspace_module.go with path traversal + symlink protection
- Permission: workspace.manage; config: WORKSPACE_ROOT, WORKSPACE_QUOTA_MB
- Runner wiring with graceful degradation (module absent if root unwritable)
- 16 new tests, all passing with -race

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/config/config.go

@@ -47,6 +47,12 @@ type Config struct {
 	S3Prefix         string // optional key prefix within bucket (e.g. "armature/")
 	S3ForcePathStyle bool   // use path-style URLs (required for MinIO, most self-hosted)
 
+	// Extension workspaces
+	// WORKSPACE_ROOT: mount point for extension-managed directories (default /data/workspaces).
+	// WORKSPACE_QUOTA_MB: per-extension quota in MB (default 0 = unlimited).
+	WorkspaceRoot    string
+	WorkspaceQuotaMB int
+
 	// Structured logging
 	// LOG_FORMAT: "text" (default, backward-compatible) or "json" (structured).
 	// LOG_LEVEL: "debug", "info" (default), "warn", "error".
@@ -143,6 +149,9 @@ func Load() *Config {
 		S3Prefix:              getEnv("S3_PREFIX", ""),
 		S3ForcePathStyle:      getEnv("S3_FORCE_PATH_STYLE", "true") == "true",
 
+		WorkspaceRoot:    getEnv("WORKSPACE_ROOT", "/data/workspaces"),
+		WorkspaceQuotaMB: getEnvInt("WORKSPACE_QUOTA_MB", 0),
+
 		SkipBundledPackages: getEnvBool("SKIP_BUNDLED_PACKAGES", false),
 		BundledPackagesDir:  getEnv("BUNDLED_PACKAGES_DIR", "/app/bundled-packages"),
 		BundledPackages:     getEnv("BUNDLED_PACKAGES", ""),