feat: encrypted secrets vault across CLI, desktop, dashboard, and backend

Local vault (apps/cli): clean-room PRMVLT01 format — Argon2id →
XChaCha20-Poly1305, AEAD-bound header, atomic writes. vault:* / secrets:*
/ inject (primora:// refs) / agent credential broker (dummy tokens in the
child, real secret on the wire) / TTL sessions / stack:* operator group.

Project vault (backend): core.project_secrets, AES-256-GCM via the
platform encryptor. Metadata-only list, audit-logged reveal, and
secret://NAME refs resolved at job delivery — refs stored, values never.

Surfaces: dashboard Vault page (+ local-vault card under the Tauri
shell), desktop vault window via IPC to the primora binary,
secrets:* --remote CLI mode, metadata/write-only MCP tools so agents
consume secrets via secret:// refs without holding plaintext.

Authored By: TDvorak <[email protected]>

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

apps/desktop/ui/index.html

@@ -27,6 +27,7 @@
       </form>
       <p id="err" class="err" hidden></p>
       <p class="hint">The desktop app renders the console served by your own server. Nothing is hosted by us.</p>
+      <p class="hint"><a href="#" id="vault-link" class="vlink">Open the local Secrets Vault</a></p>
     </main>
 
     <script type="module">
@@ -51,6 +52,11 @@
         if (saved) location.replace(saved);
       }
 
+      document.getElementById("vault-link").addEventListener("click", (e) => {
+        e.preventDefault();
+        tauri?.event.emit("open-vault");
+      });
+
       form.addEventListener("submit", async (event) => {
         event.preventDefault();
         err.hidden = true;