fix(updates): check releases for a plugin install with no .git

An archive-sourced marketplace entry ("source": "url" — this project's own)
makes Claude Code unpack the plugin rather than clone it, so the cache dir
has no .git. getUpdatesStatus probed for .git first and returned "not a git
clone; check for updates manually", skipping the entire release layer:
update_available stayed false however many releases were published, and
plugin_marketplace/plugin_name were never set, so POST /api/updates/apply's
plugin branch could never fire (it answered 409, claiming nothing newer was
published). The bug reads as "up to date", so it stayed invisible for as
long as the install happened to be current.

The plugin branch now runs BEFORE the .git probe and answers without git at
all: the repository URL comes from the marketplace manifest on disk
(known_marketplaces.json -> .claude-plugin/marketplace.json -> source.url,
null rather than a guessed host for a github owner/repo shorthand), and
package.json is the only local comparison signal. A failed release lookup
is reported as release_check, never as "nothing newer".

UI/CLI: the "not a git clone" note is gated on install_kind !== "plugin", so
the Update now button is offered where the dashboard can actually check and
apply.

docs/CLI.md

@@ -277,7 +277,7 @@ Because a lane's services are fully detached, restarting the dashboard (or `agen
 | `agenthub export [file.json]` | Full JSON data export (sessions, agents, events, tokens, workflows, dashboard runs, alert rules, pricing) — defaults to a dated filename. Re-importable via `agenthub import-data` |
 | `agenthub cleanup --hours N --days M` | Abandon active sessions idle for `N` hours and/or purge completed sessions older than `M` days |
 | `agenthub reinstall-hooks` | Rewrite the Claude Code hook entries in `~/.claude/settings.json` |
-| `agenthub update-check` | Ask the server whether a newer **release** has been published, read from the forge's own releases API (derived from the `origin` remote); falls back to a commit count against the canonical remote when no release can be read, with the reason in `release_check`. Prints the release tag against the running version, a situation note for fork/feature-branch checkouts, and the **copy-paste update command**. Reports `dev_build` when the install is ahead of the newest release, and `plugin_managed` for an install under `~/.claude/plugins/cache/`. The dashboard UI can self-apply either kind (`POST /api/updates/apply`): a fast-forwardable checkout is fast-forwarded onto the release tag, rebuilt and self-restarted; a plugin install is handed to a detached `claude plugin marketplace update` → `claude plugin update` → `plugin-bootstrap.js --force` chain instead. `/agenthub-update` remains the manual equivalent, and an already-open Claude Code session still needs `/reload-plugins` to pick up new skills and commands. Also refreshes the update banner in any open dashboard tab (same `update_status` broadcast) |
+| `agenthub update-check` | Ask the server whether a newer **release** has been published, read from the forge's own releases API (a checkout derives the repo from its `origin` remote; a plugin-cache install, which has no clone and often no `.git` at all, derives it from the marketplace manifest on disk); falls back to a commit count against the canonical remote when no release can be read, with the reason in `release_check`. Prints the release tag against the running version, a situation note for fork/feature-branch checkouts, and the **copy-paste update command**. Reports `dev_build` when the install is ahead of the newest release, and `plugin_managed` for an install under `~/.claude/plugins/cache/`. The dashboard UI can self-apply either kind (`POST /api/updates/apply`): a fast-forwardable checkout is fast-forwarded onto the release tag, rebuilt and self-restarted; a plugin install is handed to a detached `claude plugin marketplace update` → `claude plugin update` → `plugin-bootstrap.js --force` chain instead. `/agenthub-update` remains the manual equivalent, and an already-open Claude Code session still needs `/reload-plugins` to pick up new skills and commands. Also refreshes the update banner in any open dashboard tab (same `update_status` broadcast) |
 | `agenthub clear-data --yes` | Delete **all** data (schema preserved). Refuses to run without `--yes` |
 | `agenthub open` | Open the dashboard in your default browser (`open` / `xdg-open` / `start`) |
 | `agenthub version` | Print the agenthub version (also `--version` / `-v`) |