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).

client/src/lib/api.ts

@@ -2290,7 +2290,7 @@ export interface CcMdItem {
 
 /** One named artifact a plugin contributes — a skill, subagent, command or
  *  output style. `name` is the frontmatter name Claude Code addresses it by
- *  (`/ccam:ship-feature`, `subagent_type: qc-local`), falling back to the
+ *  (`/agenthub:ship-feature`, `subagent_type: qc-local`), falling back to the
  *  filename when the file declares none. */
 export interface CcPluginItem {
   name: string;
@@ -2646,7 +2646,7 @@ export interface RunStartArgs {
 }
 
 /** A lane's tmux-backed terminal run — one per lane, id is the tmux session
- *  name (`ccam-lane-<laneId>`). */
+ *  name (`agenthub-lane-<laneId>`). */
 export interface RunHandle {
   id: string;
   laneId: number | null;