feat(core): add Discord Rich Presence integration

Introduce optional Discord activity updates across config, runtime, tests, and docs so playback context appears in Discord without destabilizing app lifecycle. Tune default refresh cadence to reduce pause/resume lag during real sessions.

docs/subagents/collaboration.md

@@ -143,3 +143,8 @@ Shared notes. Append-only.
 - [2026-02-22T22:10:10Z] [codex-kiku-modal-overlay-20260222T220502Z-r4m1|codex-kiku-modal-overlay] overlap note: touching `src/core/services/field-grouping-overlay.ts` + tests to fix Kiku modal auto-shown visible overlay restore when modal closes.
 - [2026-02-22T22:07:38Z] [codex-kiku-modal-overlay-20260222T220502Z-r4m1|codex-kiku-modal-overlay] completed fix: synchronized visible-overlay state when Kiku request opens via external sender; added regression test for hidden->open->resolve->hidden visibility restoration; focused field-grouping/overlay tests passing.
 - [2026-02-22T22:11:52Z] [opencode-task103-jellyfin-main-composer-20260222T221152Z-n3p7|opencode-task103-jellyfin-main-composer] overlap note: implementing user-requested TASK-103 extraction in `src/main.ts`, `src/main/runtime/composers/jellyfin-*.ts`, composer tests, and `docs/architecture.md`; coordinating with active `codex-task103-...` session to avoid clobber.
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+## 2026-02-23
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+- [2026-02-23T01:10:27Z] [opencode-task109-discord-presence-20260223T011027Z-j9r4|opencode-task109-discord-presence] starting TASK-109 closure pass via Backlog MCP + writing-plans/executing-plans; scope validate existing Discord config/runtime/docs changes, close remaining DoD evidence, and finalize task status if gates pass.
+- [2026-02-23T01:15:39Z] [opencode-task109-discord-presence-20260223T011027Z-j9r4|opencode-task109-discord-presence] user feedback from real Discord session: status resumed to Playing with noticeable delay; tuned default `discordPresence.updateIntervalMs` from 15000 to 3000 in defaults/docs/examples and updated focused config expectations; reran focused config + discord presence tests green.