feat(cc-config): switch between Claude Code accounts, keeping the workspace

Adds a "Switch profile" button left of Backups on /settings?tool=claude-code.
A *profile* is one Anthropic account - one quota - saved under a name, so the
local `claude` CLI can be pointed at a different account without disturbing
anything else.

A switch swaps exactly two identity artifacts and nothing more: `claudeAiOauth`
inside `<CLAUDE_HOME>/.credentials.json`, and `oauthAccount` + `userID` inside
the `.claude.json` config file(s). Those files are key-merged in place, and only
where they already exist, so `projects`/`numStartups`/everything else survives.
Skills, subagents, commands, memory, plugins, marketplaces, MCP servers and
settings are never read or written here - that is what makes a switch keep the
whole workspace and change only the account. `mcpOAuth` stays put too: those are
the machine's MCP server tokens, not account identity.

Profiles are one JSON file each under `<CLAUDE_HOME>/agenthub-profiles/` (dir
0700, files 0600, atomic temp+rename) and hold live OAuth tokens, so no route
ever returns token material - `GET /profiles` answers identity metadata only.

The dashboard cannot log an account in; only `claude auth login` mints tokens.
Adding a profile is therefore always "log in from a terminal, then snapshot what
the CLI wrote". `activateProfile` re-snapshots the outgoing account first so
tokens Claude Code refreshed since its last save are not lost, and refuses
(`EUNSAVED`) to switch away from an account that was never saved - that would
discard the only copy of its credentials. A switch applies to new sessions only,
since a running session rewrites the config on exit.

Routes: GET/POST/DELETE /api/cc-config/profiles, POST /profiles/activate.

Verified: server 1420/1420 (14 new, incl. token-free responses and 0600/0700
permissions), client 459/459.

server/README.md

@@ -677,6 +677,10 @@ Reads — and carefully gated mutations for low-risk text-file artifacts — for
 | `GET`    | `/api/cc-config/backups[?scope=&type=]` | Listing of all timestamped backups. Also lists `scope:"auto-memory"` backups (each carrying `project`) |
 | `PUT`    | `/api/cc-config/file`                 | Create or overwrite a text-file artifact (skills/agents/commands/output-styles/memory). Body: `{ scope, type, name?, content }`. Auto-backs-up if file exists. Atomic temp + rename. 256 KB cap. Per-project file-based memory is also editable via `{ scope: "auto-memory", type: "auto-memory", project, name }` — backups land under `<memory-dir>/.cc-config-backups/auto-memory/`, and an invalid project slug returns `EBADPROJECT` |
 | `DELETE` | `/api/cc-config/file`                 | Backup-then-delete a text-file artifact. Skill dirs are backed up whole before recursive removal |
+| `GET`    | `/api/cc-config/profiles`             | `{ items, active }` — saved auth profiles + the account logged in right now. Identity metadata only, **never token material** |
+| `POST`   | `/api/cc-config/profiles`             | Snapshot the logged-in account as a profile. Body: `{ name }`. `ENOAUTH` when nobody is logged in |
+| `POST`   | `/api/cc-config/profiles/activate`    | Make a saved profile the live account — swaps `claudeAiOauth` + `oauthAccount`/`userID` and nothing else. Body: `{ name }`. Re-snapshots the outgoing account first (`savedOutgoing`); `EUNSAVED` if it was never saved |
+| `DELETE` | `/api/cc-config/profiles`             | Forget a saved profile. Body: `{ name }`. `EACTIVE` for the active one |
 
 ### Run a lane's CLI (`/api/run`)