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/data/pipelines/default.json

@@ -1,14 +1,14 @@
 {
   "id": "default",
   "name": "Default feature pipeline",
-  "skill": "/ccam:ship-feature",
+  "skill": "/agenthub:ship-feature",
   "nodes": [
     {
       "id": "intake",
       "label": "Intake",
       "icon": "📝",
       "gate": false,
-      "command": "ccam stage intake",
+      "command": "agenthub stage intake",
       "aliases": [
         "assigned",
         "claimed",
@@ -176,7 +176,7 @@
       "label": "Done",
       "icon": "✅",
       "gate": false,
-      "command": "ccam stage done",
+      "command": "agenthub stage done",
       "aliases": [
         "complete",
         "completed",