feat(host): Keychain and Credential Manager token stores, a macOS/Windows CI job (P11a step 0)

The agent path was Linux-only because tokens had a keyring store only
there (every other OS hit NOT_YET, so `connect` and the bridge failed).
D-56's destination is one installation for macOS, Windows and Linux.
Both new stores sit behind the same Items trait as the Secret Service,
so INVARIANT 4 (one account, one item, locked is an error) is kept once
and tested once through the file keyring. Windows credentials have a
unique target name, so a probe stands in for a search.

New dependencies (ledger-host only, target-gated): apple-native-keyring-store
(feature keychain) and windows-native-keyring-store, the stores the
keyring-core 1 API we already use is published with. No ledger-core change.

The `portable` job builds and tests the workspace on macos-latest and
windows-latest. Windows is allowed to fail: the rest of the host is
Unix-only (inventory in docs/packaging.md). Not verified locally: no
macOS or Windows target is installed; CI is the evidence.

Also pins cargo-packager, cargo-packager-updater and cargo-generate-rpm
in mise.toml for the trial, and records that the trial is not yet run.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HS8WZziDnyxunC23MUxrLp

README.md

@@ -67,10 +67,11 @@ Sheet is frozen as of 2026-10-11. The remaining work, its order and its
 hand-off are `plan/served.md` section 8.0; the destination is one
 installed app for Mac, Windows and Linux (P11), then the hosted service
 the plan describes and does not build. Today the agent path runs on
-Linux: tokens live in the OS keyring and only the Linux Secret Service
-store exists, so on macOS the viewer and server run but `wanderbooks
-connect` and the agent bridge wait for P11's keyring stores; Windows is
-WSL2 only.
+Linux: tokens live in the OS keyring (the Secret Service on Linux, the
+login Keychain on macOS, the Credential Manager on Windows; the last two
+are written and compiled by the CI matrix, P11a step 0, and not yet
+proven on a machine of ours); the rest of the host is Unix-only, so
+Windows is WSL2 only until its sockets and data root are ported.
 
 See [`plan/STATUS.md`](plan/STATUS.md) for where things stand and
 [`plan/roadmap.md`](plan/roadmap.md) for where it's going.
@@ -90,8 +91,9 @@ curl -fsSL https://wanderbooks.ai/install.sh | sh -s -- acme
 ```
 
 (Linux today. On macOS the same line installs and sets up, and the
-viewer runs, but connecting an agent waits for P11's keyring store; on
-Windows run it inside WSL2.)
+viewer runs; connecting an agent uses the login Keychain, new with
+P11a step 0 and proven only by the CI matrix so far. On Windows run it
+inside WSL2.)
 
 Already installed, three commands: `wanderbooks setup`, `wanderbooks books
 create acme`, `wanderbooks connect claude --book acme` (or `connect codex`).