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/codex-nudge.js

@@ -4,7 +4,7 @@
  * from its rollout journal — that keeps the pipeline map moving, but an
  * inferred stage carries no evidence, so its node renders
  * `passed-no-evidence` (amber) rather than `done`. Only the session's own
- * `ccam stage <node> --evidence "..."` call can supply that, and a codex
+ * `agenthub stage <node> --evidence "..."` call can supply that, and a codex
  * session has no hook or wrapper that does it for it.
  *
  * This module never writes `stage`, `stages` or `detected_stage` itself. It
@@ -65,7 +65,7 @@ function sweepCodexNudges() {
 
       tmux.sendText(
         runId,
-        `[ccam] Stage "${lane.stage}" was inferred and has no evidence — run: ccam stage ${lane.stage} --tool codex --evidence "..."`
+        `[agenthub] Stage "${lane.stage}" was inferred and has no evidence — run: agenthub stage ${lane.stage} --tool codex --evidence "..."`
       );
       nudgedFor.set(lane.id, lane.stage);
       nudged += 1;