Address Gadfly review findings on Phase 0

Applied the fixes warranted by the adversarial review of PR #21 (all
findings graded in the gadfly store):

Store (highest impact):
- buildDSN always merges busy_timeout/journal_mode/foreign_keys pragmas
  into the DSN, even for file: URIs or paths with a query string — the
  prior passthrough silently disabled FK enforcement for those PANSY_DB
  values. Also escape '#' in the path and tighten in-memory detection to
  an exact ':memory:' token or mode=memory param (no substring misfire).
- migrate.go: detect duplicate migration versions with a clear error;
  wrap appliedVersions' rows.Err() with the store: prefix.

API:
- SetTrustedProxies failure now falls back to trust-none instead of
  leaving gin's trust-everyone default (X-Forwarded-For spoofing).
- SPA: 404 embedded directories (was a directory listing), 404 bare /api,
  add X-Content-Type-Options: nosniff, cache index.html bytes once at
  startup, single fs.Stat existence check, shared writeAPIError helper.
- Move gin.SetMode out of package init() into New().

Config: validate PANSY_PORT range (fall back to 8080 with a warning).

Web:
- api.ts: serialize the request body before the fetch try so a
  JSON.stringify failure isn't misreported as a network error.
- AppShell: move state-specific/conflicting utilities into
  active/inactiveProps so concatenated Tailwind classes don't collide.

Tests: added store DSN-pragma/memory-detection cases and SPA
directory-404 case. go build/vet/test clean (CGO off); web tsc + build
clean; re-verified in a browser (SPA, deep links, /assets 404, nav).

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_01JdQpdYYsTgtkJBxbcpAszi

internal/api/api.go

@@ -15,21 +15,22 @@ import (
 	"gitea.stevedudenhoeffer.com/steve/pansy/internal/config"
 )
 
-func init() {
-	// Quiet gin's default debug output; we log via slog-gin instead.
-	gin.SetMode(gin.ReleaseMode)
-}
-
 // New builds the gin engine with the standard middleware stack and registers the
 // API routes. The embedded SPA fallback is registered separately by the caller
 // via RegisterSPA (see spa.go) so the API can be built and tested without a web
 // build present.
 func New(cfg *config.Config) *gin.Engine {
+	gin.SetMode(gin.ReleaseMode)
+
 	r := gin.New()
 	r.Use(sloggin.New(slog.Default()), gin.Recovery())
 
 	if err := r.SetTrustedProxies(cfg.TrustedProxies); err != nil {
-		slog.Warn("api: failed to set trusted proxies", "error", err)
+		// Do not leave gin's trust-everyone default active on a parse failure —
+		// that would let any client spoof X-Forwarded-For. Fall back to trusting
+		// no proxies, which is also the behavior when none are configured.
+		slog.Error("api: invalid trusted proxies, trusting none", "error", err)
+		_ = r.SetTrustedProxies(nil)
 	}
 
 	v1 := r.Group("/api/v1")