refactor!: rebrand CCAM to AgentHub

Clean break, no compatibility alias. Renames the product name, the CLI
binary (`ccam` -> `agenthub`), the env var prefix (`CCAM_` ->
`AGENTHUB_`), the Prometheus metric namespace (`ccam_*` ->
`agenthub_*`), the tmux session prefix (`ccam-lane-<id>` ->
`agenthub-lane-<id>`), the per-repo runtime profile directory
(`.ccam/profile` -> `.agenthub/profile`), the lanes state root
(`~/.claude/ccam-lanes` -> `~/.claude/agenthub-lanes`), the bundled
plugins (`plugins/ccam*` -> `plugins/agenthub*`) and their slash
commands (`/ccam-doctor` -> `/agenthub-doctor`, `/ccam:*` ->
`/agenthub:*`).

Because there is no alias, an existing install has to be updated by
hand: rename its `.ccam/profile` directory and any `CCAM_*` variables,
and reinstall the plugin under its new name.

Two other name families are deliberately left alone here, since they are
not just strings: the `Claude-Code-Monitor` repository/marketplace name,
and the `agent-dashboard` npm package plus its `~/.claude/agent-dashboard`
runtime directory, which holds the live database and needs a migration
rather than a rename.

Verified: server 1406/1406, client 459/459, `grep -i ccam` clean across
tracked files, `openapi.yaml` regenerated (95 paths, unchanged count).

plugins/agenthub/commands/agenthub-open.md

@@ -0,0 +1,32 @@
+---
+description: Rebuild the dashboard UI and print its URL
+---
+
+Rebuild the dashboard bundle, then print the URL. Always forces a rebuild so a
+stale bundle (e.g. after a fix commit landed but the bootstrap's build predates
+it) never serves silently. Also finishes the build if the bootstrap's own
+attempt failed (check `~/.claude/agent-dashboard/runtime/client-build.log`).
+
+```bash
+node "${CLAUDE_PLUGIN_ROOT}/scripts/plugin-open.js" --force
+```
+
+Install + build takes a few minutes if the client toolchain isn't already
+installed; otherwise the rebuild itself takes ~10-15s. The server serves from
+that directory, so it usually needs no restart — but if it is down, or still
+running from a plugin root a mid-session `/plugin` update retired, the command
+re-runs bootstrap first and prints `Server restarted on the current plugin
+version.` (without it, the fresh bundle would call routes that old server
+never had).
+
+Then help the user open it:
+
+```bash
+uname -s
+```
+
+- `Darwin` → `open <url>`
+- `Linux` → `xdg-open <url>`
+- otherwise → tell them to open the URL in a browser.
+
+Keep the output to a few lines.