feat(cli): Add an anonymous Snake leaderboard

[sergical]

Adds sentry games leaderboard, which shows the top 10 Snake scores from the last 30 days. Stacked on #1435.

Scores (CLI)

• A finished game sends one snake.score metric to the CLI telemetry project. Its only custom attribute is a random handle such as brave-otter-42, stored in the local metadata table.
• The metric goes out in a new trace with the user cleared on both scopes. beforeSendMetric keeps only handle, sentry.release, sentry.environment and sentry.sdk.* for this metric.
• Nothing is sent when telemetry is off (SENTRY_CLI_NO_TELEMETRY, DO_NOT_TRACK, or the stored preference).

Endpoint (sentry-mcp Worker)

• GET /api/games/snake/leaderboard queries the tracemetrics dataset for max(value) per handle, with value:<=10000.
• It rate-limits by hashed IP (30/min) and caches the result in KV for 5 minutes.
• It checks the upstream rows against the handle format and the score bounds. Every failure returns a generic error. The token, URL and upstream text never reach the response or the logs.
• The CLI validates each row again and drops rows that fail, so server text cannot write control sequences to the terminal.

Setup before deploy

1. Create a token on a bot account that is only a member of the team that owns the CLI project, with the org:read scope only.
2. npx wrangler secret put SENTRY_GAMES_READ_TOKEN from packages/mcp-cloudflare.
3. Optional: turn on "Prevent storing IP addresses" on the CLI project. This also affects the rest of the CLI telemetry.

Known limit: the DSN is public, so anyone can submit a score. The handle format and the 10,000 cap block only impossible values.

Breaking Changes: None