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).

package.json

@@ -2,9 +2,9 @@
   "name": "agent-dashboard",
   "version": "1.4.6",
   "bin": {
-    "ccam": "bin/ccam.js"
+    "agenthub": "bin/agenthub.js"
   },
-  "description": "Real-time dashboard for tracking Claude Code agent activity",
+  "description": "Local control surface for Claude Code agents - session monitoring, parallel lanes, terminal runs, and Claude Code configuration management",
   "private": true,
   "type": "commonjs",
   "main": "server/index.js",
@@ -84,7 +84,7 @@
     "format": "prettier --write .",
     "format:check": "prettier --check .",
     "openapi:yaml": "node scripts/generate-openapi-yaml.js",
-    "link-cli": "npm link || node -e \"console.warn('ccam CLI not linked globally (no permission?). Link manually with: npm link')\"",
+    "link-cli": "npm link || node -e \"console.warn('agenthub CLI not linked globally (no permission?). Link manually with: npm link')\"",
     "docker:up": "docker compose up -d --build",
     "docker:down": "docker compose down"
   },