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

web/src/lib/api.ts

@@ -84,6 +84,10 @@ function messageFrom(body: unknown, status: number): string {
 export async function apiFetch<T>(path: string, opts: RequestOptions = {}): Promise<T> {
   const { method = 'GET', body, params, signal } = opts
 
+  // Serialize before the try so a JSON.stringify failure (e.g. a circular value)
+  // surfaces as itself, not as a misleading "cannot reach the server" error.
+  const requestBody = body !== undefined ? JSON.stringify(body) : undefined
+
   let res: Response
   try {
     res = await fetch(buildUrl(path, params), {
@@ -94,7 +98,7 @@ export async function apiFetch<T>(path: string, opts: RequestOptions = {}): Prom
         accept: 'application/json',
         ...(body !== undefined ? { 'content-type': 'application/json' } : {}),
       },
-      body: body !== undefined ? JSON.stringify(body) : undefined,
+      body: requestBody,
     })
   } catch (err) {
     if ((err as Error)?.name === 'AbortError') throw err