items 5-7: passkey step-up, tools enable/disable, note RAG — end to end

Completes the three in-flight open items and fixes the away-fallthrough bug.

Item 7 — passkey step-up (WebAuthn):
- internal/webauthn: ES256/P-256 register + assert with real ecdsa signature
  verification, minimal CBOR/COSE decode, PasskeySession (L2→L3 on assert,
  decays after TTL). Drop the RS256 offer we can't verify (register-ok/
  assert-fail trap). Verify rpIdHash + UP/UV flags in FinishAssertion — UV is
  the step-up gesture. Round-trip test with negative cases (tampered sig,
  missing UV, wrong origin).
- cmd/mavweb: /auth/passkey enroll+assert page (the only surface that can do
  a WebAuthn gesture) + the four begin/finish endpoints. Without this the
  daemon's PasskeySession swap leaves /tools enable permanently blocked.
- daemon wires PasskeySession as the auth Session + srv.StepUp; policy gates
  MethodAssertStepUp at AuthRead.

Item 5 — tools page: DisableTool through store/ipc/client/wire; /tools grows a
disable action and a link to the passkey page. Lifecycle test.

Item 6 — note RAG: PhraseQuery on the phraser (LLM-composed answer over top-k
notes, raw-notes fallback); IntentQuery routes through it. Stub returns a
deterministic summary.

Item 2 — away-fallthrough: on ErrVoiceNoSession the dispatcher now reroutes
through the AWAY table (sev3→ntfy, sev4→telegram-repeat-til-ack, sev≤2→drop)
instead of silently dropping / mis-routing to the present-list remainder.
Covers DispatchNudge + DispatchReminder. 4 tests.

Also: re-add ProposeTool to CoreAPI (dropped in a comment rewrite), fix
missing imports + a duplicate block left mid-edit, drop dead AssertStepUpFunc,
gitignore /mavcaldav.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitignore

@@ -5,6 +5,7 @@
 /mavttsd
 /mavweb
 /mavpoll
+/mavcaldav
 
 # Certs (private keys, don't commit)
 certs/