feat(runtime): track user-level Pi configuration with the provider key templated

Mirrors ~/.pi/agent/ as the authoritative copy. models.json becomes
models.json.template with ${ZENMUX_API_KEY} substituted; the real value stays
in secrets/zenmux.env, which is untracked and enforced by the pre-commit guard.

Excluded with rationale: auth.json, trust.json, models-store.json, sessions/,
herdr-agent-state.ts (installer-managed, overwritten on reinstall) and the
third-party skills under ~/.agents/skills.

Recorded during migration: the configured fallback model zenmux/x-ai/grok-4.6 is
absent from models.json, so pi falls back to an undeclared custom model id with
no context window, cost table or thinkingLevelMap. Fixing that is a behaviour
change and is deferred rather than folded into this zero-change migration.

runtime/agent/extensions/pi-memo-trust.ts

@@ -0,0 +1,21 @@
+import type {
+  ExtensionAPI,
+  ProjectTrustEventResult,
+} from "@earendil-works/pi-coding-agent";
+import { realpathSync } from "node:fs";
+import { resolve } from "node:path";
+
+const MEMO_WORKSPACE = "/home/claw/pi-workspaces/memo-inbox";
+
+export default function piMemoTrust(pi: ExtensionAPI) {
+  pi.on("project_trust", async (event): Promise<ProjectTrustEventResult> => {
+    try {
+      if (realpathSync(resolve(event.cwd)) === realpathSync(MEMO_WORKSPACE)) {
+        return { trusted: "yes", remember: true };
+      }
+    } catch {
+      // Fall through to Pi's normal trust decision for every other path.
+    }
+    return { trusted: "undecided" };
+  });
+}