feat: add gbrain check-update command and auto-update agent workflow (#15)

* feat: add `gbrain check-update` command for auto-update notifications

Deterministic collector that checks GitHub Releases for new versions,
compares semver (minor+ only, skips patches), and fetches changelog diffs.
Exports `detectInstallMethod()` from upgrade.ts for reuse. Includes 15
unit tests covering version comparison, CLI wiring, and error handling.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* test: add E2E upgrade tests against real GitHub API

Exercises check-update CLI end-to-end: valid JSON output, human-readable
mode, help text, graceful no-releases handling, and version comparison
wiring. Skips gracefully when network is unavailable.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* docs: add SKILLPACK Section 17 — auto-update notifications

Full agent playbook for the update lifecycle: check, notify, consent,
upgrade, skills refresh, schema sync, report. Includes standalone
self-update for skillpack-only users via version markers and raw
GitHub URL fetching. Adds version markers to both SKILLPACK and
RECOMMENDED_SCHEMA headers.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat: add auto-update step 7 to install paste, setup Phase G, migrations dir

Adds step 7 to the OpenClaw install paste (default-on update checks).
Setup skill gets Phase G (conditional offer for manual installs) and
schema state tracking via ~/.gbrain/update-state.json. Creates
skills/migrations/ directory for version-specific upgrade directives.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* docs: update CLAUDE.md with E2E test DB lifecycle, migration conventions

Adds E2E test DB lifecycle instructions (spin up, run, tear down).
Documents version migration convention (skills/migrations/v[version].md)
and schema state tracking (~/.gbrain/update-state.json). Updates test
file counts.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix: broken semver comparison in extractChangelogBetween

The version range check compared minor versions without guarding on
major being equal, causing incorrect changelog entries to be captured
(e.g., v0.5.0 would match when upgrading from v1.2.0). Extracted
semverGt/semverLte helpers for correct comparisons. Added 5 tests
for extractChangelogBetween covering cross-major, same-version, and
malformed input cases.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* chore: bump version and changelog (v0.4.1)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -2,6 +2,28 @@
 
 All notable changes to GBrain will be documented in this file.
 
+## [0.4.1] - 2026-04-09
+
+### Added
+
+- `gbrain check-update` command with `--json` output. Checks GitHub Releases for new versions, compares semver (minor+ only, skips patches), fetches and parses changelog diffs. Fail-silent on network errors.
+- SKILLPACK Section 17: Auto-Update Notifications. Full agent playbook for the update lifecycle: check, notify, consent, upgrade, skills refresh, schema sync, report. Never auto-upgrades without user permission.
+- Standalone SKILLPACK self-update for users who load the skillpack directly without the gbrain CLI. Version markers in SKILLPACK and RECOMMENDED_SCHEMA headers, with raw GitHub URL fetching.
+- Step 7 in the OpenClaw install paste: daily update checks, default-on. User opts into being notified about updates, not into automatic installs.
+- Setup skill Phase G: conditional auto-update offer for manual install users.
+- Schema state tracking via `~/.gbrain/update-state.json`. Tracks which recommended schema directories the user adopted, declined, or added custom. Future upgrades suggest new additions without re-suggesting declined items.
+- `skills/migrations/` directory convention for version-specific post-upgrade agent directives.
+- 20 unit tests and 5 E2E tests for the check-update command, covering version comparison, changelog extraction, CLI wiring, and real GitHub API interaction.
+- E2E test DB lifecycle documentation in CLAUDE.md: spin up, run tests, tear down. No orphaned containers.
+
+### Changed
+
+- `detectInstallMethod()` exported from `upgrade.ts` for reuse by `check-update`.
+
+### Fixed
+
+- Semver comparison in changelog extraction was missing major-version guard, causing incorrect changelog entries to appear when crossing major version boundaries.
+
 ## [0.4.0] - 2026-04-09
 
 ### Added