feat(v0.6.3): release-update notifier (notify-only, SessionStart)

Adds a lightweight "new release available" notice without auto-installing —
because re-running install.sh overwrites ADAM's own /reflect-applied skill
edits, so the user must choose when to take an update.

- install.sh writes ~/.claude/adam/.version (the installed release tag) on
  every install. Derived from $VERSION / piped REF / `git describe --tags`.
- adam-nudge.mjs (SessionStart) compares .version against the latest GitHub
  release at most once/day. Cached in ~/.claude/adam/.update-check.json; the
  cache drives an instant nudge (no network on the hot path) and is refreshed
  best-effort with a 1.5s AbortController cap. fetch unavailable / offline /
  timeout / rate-limit / parse error all degrade to silent no-op. Opt out with
  ADAM_NO_UPDATE_CHECK=1. main() is now async; never blocks SessionStart.
- README: "Staying up to date" section; pin example bumped to v0.6.3.

Tests: 134 -> 138. Notifier verified fully offline (cache-driven): nudges when
a newer release is cached, silent when current, suppressed by the opt-out env,
and no-ops when the .version marker is absent.

agents/adam.md

@@ -516,7 +516,7 @@ MOSS's core thesis: "routing, hook ordering, state invariants, and dispatch live
 2. `cross_session_evidence == true` (≥5 occurrences across ≥3 sessions)
 3. `auto_apply_eligible: false` — **always**. Harness edits are never auto-applied.
 4. `blast_radius: high`
-5. Proposal includes a `# Test verification` section with the command `bash ~/.claude/adam/tests/run-tests.sh` and the expected result "134 passed, 0 failed" (or current pass count). The skill runs this test before applying.
+5. Proposal includes a `# Test verification` section with the command `bash ~/.claude/adam/tests/run-tests.sh` and the expected result "138 passed, 0 failed" (or current pass count). The skill runs this test before applying.
 6. Change is surgical: ≤30 LOC diff, single file.
 7. `# Diagnosis` reconstructs the causal chain from harness-level behavior (not from text-artifact behavior). The mismatch must name a specific code path (function, regex, threshold) in the target file.