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.

client/src/pages/__tests__/__snapshots__/screens.snapshot.test.tsx.snap

@@ -795,6 +795,61 @@ exports[`screen snapshots > Claude Config 1`] = `
               Project
             </button>
           </div>
+          <button
+            class="inline-flex items-center gap-2 rounded-lg border border-border bg-surface-2 px-3 py-1.5 text-xs font-medium text-fg-secondary hover:bg-surface-3 transition-colors"
+          >
+            <svg
+              class="lucide lucide-user-cog w-3.5 h-3.5"
+              fill="none"
+              height="24"
+              stroke="currentColor"
+              stroke-linecap="round"
+              stroke-linejoin="round"
+              stroke-width="2"
+              viewBox="0 0 24 24"
+              width="24"
+              xmlns="http://www.w3.org/2000/svg"
+            >
+              <circle
+                cx="18"
+                cy="15"
+                r="3"
+              />
+              <circle
+                cx="9"
+                cy="7"
+                r="4"
+              />
+              <path
+                d="M10 15H6a4 4 0 0 0-4 4v2"
+              />
+              <path
+                d="m21.7 16.4-.9-.3"
+              />
+              <path
+                d="m15.2 13.9-.9-.3"
+              />
+              <path
+                d="m16.6 18.7.3-.9"
+              />
+              <path
+                d="m19.1 12.2.3-.9"
+              />
+              <path
+                d="m19.6 18.7-.4-1"
+              />
+              <path
+                d="m16.8 12.3-.4-1"
+              />
+              <path
+                d="m14.3 16.6 1-.4"
+              />
+              <path
+                d="m20.7 13.8 1-.4"
+              />
+            </svg>
+            Switch profile
+          </button>
           <button
             class="inline-flex items-center gap-2 rounded-lg border border-border bg-surface-2 px-3 py-1.5 text-xs font-medium text-fg-secondary hover:bg-surface-3 transition-colors"
           >