fix(call-to-play): let callers start before the roster fills

The card hid Start now until the roster filled or the deadline elapsed,
preventing groups from starting early with fewer players. Expose the existing
start action for every unfinished caller-owned call, including scheduled calls
before check-in. Keep check-in controls and launch only after core acceptance.

Add rendered-card regressions for six-of-eight players, solo and scheduled
starts, creator authority, terminal states, and unavailable local games. Use
installed React packages for these tests without rewriting the app lockfile,
and document the caller's control over start time.

Test Plan:
- `just frontend-test` -- passed, 107 tests including 8 rendered-card tests
- `just test` -- passed, 797 Rust tests
- `just clippy` -- passed with warnings denied
- `just fmt` -- passed
- `deno task build` -- passed TypeScript and Vite production build
- `git diff --cached --check` -- passed

crates/lanspread-tauri-deno-ts/deno.test.json

@@ -0,0 +1,9 @@
+{
+  "nodeModulesDir": "manual",
+  "lock": false,
+  "compilerOptions": {
+    "jsx": "react-jsx",
+    "jsxImportSource": "react",
+    "lib": ["deno.window", "dom", "dom.iterable"]
+  }
+}