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

README.md

@@ -91,6 +91,10 @@ just test
 just frontend-test
 ```
 
+Frontend tests render components with the React packages installed by
+`just setup`. Their separate Deno configuration uses those installed packages
+without rewriting the application's dependency lockfile.
+
 See [launcher shutdown ownership](crates/lanspread-tauri-deno-ts/SHUTDOWN.md)
 for the cancellation/drain sequence and a native close-button regression probe.
 
@@ -319,7 +323,7 @@ just peer-cli-charlie
 | `just fmt`                                          | Format Rust, TOML, Markdown, and the Justfile.                           |
 | `just clippy`                                       | Lint every Rust workspace target with warnings denied.                   |
 | `just test`                                         | Run every Rust workspace test target.                                    |
-| `just frontend-test`                                | Run the frontend reducer/lifecycle tests.                                |
+| `just frontend-test`                                | Run frontend reducer, lifecycle, and rendered component tests.           |
 | `just peer-cli-build`                               | Build the JSONL peer harness.                                            |
 | `just peer-cli-image`                               | Check fixture authority and build the harness Docker image.              |
 | `just peer-cli-tests [SCENARIO ...]`                | Run selected scenarios, or the complete matrix when no IDs are supplied. |