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).

scripts/plugin-open.js

@@ -4,7 +4,7 @@
  * @description Builds the dashboard UI bundle for a plugin install and prints
  * the dashboard URL. `scripts/plugin-bootstrap.js` calls `buildClient` eagerly
  * on session start, so client-only routes (e.g. `/run`) work the moment
- * `claude` is started, not just the API and MCP tools. `/ccam-open` re-runs
+ * `claude` is started, not just the API and MCP tools. `/agenthub-open` re-runs
  * this standalone — a no-op when the bundle already matches — as a fallback
  * for `--force` rebuilds or a first build that failed during bootstrap, and it
  * re-runs bootstrap first when the live server belongs to a retired plugin root