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).

server/lib/proof.js

@@ -5,7 +5,7 @@
  * `lane_features` already tracks. Ported from Shipyard's
  * `dashboard/server/services/proof.js`; the "current feature" special-casing
  * that file needed (it has no DB, so it parsed a branch regex) is dropped —
- * CCAM's `lane_features` row already IS that source of truth.
+ * AgentHub's `lane_features` row already IS that source of truth.
  *
  * Path containment is the entire security surface here: every path this
  * module touches is resolved, realpath'd, and checked to be inside the
@@ -249,7 +249,7 @@ function deleteProof(laneId, { slug, group, images } = {}) {
  * already points at the right place.
  *
  * Never auto-invoked by this codebase; exposed only as the explicit
- * `ccam lanes proof-link` primitive.
+ * `agenthub lanes proof-link` primitive.
  *
  * @param {object} lane - A hydrated lane row (must have `cwd`).
  * @returns {{linked: boolean}} `linked: false` when nothing changed.