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).

.devcontainer/devcontainer.json

@@ -1,6 +1,6 @@
 {
   // ─────────────────────────────────────────────────────────────────────────
-  // Optional, opt-in dev environment for Claude Code Agent Monitor.
+  // Optional, opt-in dev environment for AgentHub.
   // Used only when you choose "Dev Containers: Reopen in Container" (VS Code) or
   // open the repo in a GitHub Codespace. It changes nothing for host-based dev.
   //
@@ -13,7 +13,7 @@
   // installer refuses to run inside a container. Run `npm run install-hooks` on
   // your host so hooks POST to http://localhost:4820 (forwarded from here).
   // ─────────────────────────────────────────────────────────────────────────
-  "name": "Claude Code Agent Monitor",
+  "name": "AgentHub",
   "build": {
     "dockerfile": "Dockerfile",
     "context": ".."