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/lane-sync.js

@@ -190,10 +190,10 @@ async function unmergedFiles(cwd) {
  *  already established. */
 async function setupMergeDriver(cwd, generatedPaths) {
   if (!generatedPaths.length) return;
-  await git(cwd, ["config", "merge.ccam-generated.driver", "true"]);
+  await git(cwd, ["config", "merge.agenthub-generated.driver", "true"]);
   await git(cwd, [
     "config",
-    "merge.ccam-generated.name",
+    "merge.agenthub-generated.name",
     "keep ours; regenerated post-merge by the profile regen hook",
   ]);
 
@@ -204,7 +204,7 @@ async function setupMergeDriver(cwd, generatedPaths) {
   const lines = new Set(existing.split("\n").filter(Boolean));
   let changed = false;
   for (const gp of generatedPaths) {
-    const line = `${gp} merge=ccam-generated`;
+    const line = `${gp} merge=agenthub-generated`;
     if (!lines.has(line)) {
       lines.add(line);
       changed = true;