#5201: Signal: add group mention gating with requireMention config

Implements per-group mention gating for Signal channels, allowing bots to selectively respond only when mentioned in group chats. ## Features - Add `channels.signal.groups.<groupId>.requireMention` config option - Support wildcard default with `channels.signal.groups["*"]` - **Signal native @ mentions**: Fully supported - detects mentions using Signal's mentions metadata (phone number/UUID matching) - **Text-based patterns**: Also supported via `mentionPatterns` config (e.g., "bot", "@bot", emojis) - Store non-mentioned messages in history context - Full multi-account support with per-account group configs - Multi-bot support: Each bot only responds to their own mentions - Comprehensive test coverage (unit + integration tests: 13/13 passing) ## Configuration example ```json5 { channels: { signal: { groups: { "*": { requireMention: true }, "specific-group": { requireMention: false } } } }, messages: { groupChat: { mentionPatterns: ["@bot", "bot", "🦞"] } } } ``` ## Testing Added comprehensive test coverage: - Unit tests for `resolveSignalGroupRequireMention()` function (8 tests) - Integration tests for event handler mention gating logic (5 tests) - Tests follow existing repository patterns - All tests passing ✅ ## Documentation Updated Signal documentation with: - Configuration examples for group mention gating - Explanation of both Signal native mentions and text pattern support - Multi-account configuration examples ## Implementation Details - Added `SignalMention` type with `start`, `length`, `number`, and `uuid` fields - Parses Signal's `dataMessage.mentions` array to detect bot-specific mentions - Combines native mention detection with existing text pattern matching - Only triggers when the bot's own account (phone/UUID) is mentioned ## CI Notes ⚠️ **Lint failures**: The failing lint checks (`no-base-to-string`, `restrict-template-expressions`) are **pre-existing** in `src/commands/onboard-auth.credentials.ts` and `src/commands/auth-choice.apply.oauth.ts` - they exist on main branch and are unrelated to this PR's changes. All tests related to this feature pass successfully. Follows existing patterns from WhatsApp and Telegram channels. Fixes #1184 <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> Adds per-group mention gating for Signal by introducing `channels.signal.groups.<groupId>.requireMention` (with `"*"` wildcard support) and wiring mention-gating checks into the Signal SSE receive event handler. The handler now evaluates both text-based mentionPatterns and Signal native `dataMessage.mentions` metadata to decide whether to dispatch an inbound group message, while still recording skipped messages into group history for context. Also extends Signal config types/zod schema to include per-group settings and adds unit/integration tests plus docs/changelog updates. <h3>Confidence Score: 3/5</h3> - Moderately safe to merge, but has a likely correctness bug in native mention UUID matching and some behavior/documentation mismatches. - Core change is localized and covered by tests, but the native mention detection compares `mention.uuid` to `deps.accountId` (config identifier) which is unlikely to match Signal UUIDs, causing mention gating to incorrectly skip messages in real use. History recording also misses non-text message bodies, and one config comment contradicts observed default behavior. - src/signal/monitor/event-handler.ts (mention matching + history recording), src/config/types.signal.ts (default behavior documentation) <!-- greptile_other_comments_section --> _{(2/5) Greptile learns from your feedback when you react with thumbs up/down!} **Context used:** - Context from `dashboard` - CLAUDE.md ([source](https://app.greptile.com/review/custom-context?memory=fd949e91-5c3a-4ab5-90a1-cbe184fd6ce8)) - Context from `dashboard` - AGENTS.md ([source](https://app.greptile.com/review/custom-context?memory=0d0c8278-ef8e-4d6c-ab21-f5527e322f13)) <!-- /greptile_comment -->