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/routes/workflows.js

@@ -95,7 +95,7 @@ router.get("/skill-usage", (req, res) => {
     for (const m of mcpCalls) {
       // mcp__plugin_<plugin>_<server>__<tool>. Both halves may contain
       // underscores, so the split is only unambiguous when the plugin names its
-      // server after itself — the overwhelmingly common case (`ccam_ccam`,
+      // server after itself — the overwhelmingly common case (`agenthub_agenthub`,
       // `vercel_vercel`), which the dedupe below collapses back to one name.
       // ponytail: a plugin whose server has its own name reports under
       // "<plugin>_<server>"; read the real pairing off the MCP config if that