feat(stockholm): add Go backend integration for Stockholm frontend

Implements pkg/service/stockholm with bridge (appSend/runQueue), HTTP
proxy, static serving, config URL rewriting, native state persistence,
and device discovery. Mounts under a configurable base path (/stockholm
by default) with correct http.StripPrefix routing and apiBase-prefixed
bridge API routes matching the patched JS window.__stockholmBase calls.

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

scripts/patch-stockholm-bridge.py

@@ -0,0 +1,39 @@
+#!/usr/bin/env python3
+"""Patch Stockholm bridge JS files to use window.__stockholmBase for API paths.
+
+Usage: patch-stockholm-bridge.py <file> [<file> ...]
+
+Applied once by `make prepare-stockholm`. Idempotent — already-patched files
+are left unchanged.
+"""
+import sys
+
+REPLACEMENTS = [
+    (
+        'xhr.open("POST", "/api/native/appSend"',
+        'xhr.open("POST", (window.__stockholmBase||"") + "/api/native/appSend"',
+    ),
+    (
+        'xhr.open("GET", "/api/native/runQueue',
+        'xhr.open("GET", (window.__stockholmBase||"") + "/api/native/runQueue',
+    ),
+    (
+        'var proxyPath = "/api/http-proxy";',
+        'var proxyPath = (window.__stockholmBase||"") + "/api/http-proxy";',
+    ),
+    (
+        'return new URL(url, window.location.origin + "/").href;',
+        'return new URL(url, window.location.origin + (window.__stockholmBase || "") + "/").href;',
+    ),
+]
+
+for path in sys.argv[1:]:
+    try:
+        original = open(path).read()
+        patched = original
+        for old, new in REPLACEMENTS:
+            patched = patched.replace(old, new)
+        if patched != original:
+            open(path, "w").write(patched)
+    except FileNotFoundError:
+        print(f"warning: {path} not found, skipping", file=sys.stderr)