fix(chat): kill fake user bubble + stuck thinking state after /compact

[itsdestin]

Re-opens #100 — same branch, rebased onto green master now that PR #101 unblocked CI.

Summary

• Bug Planned Updates Tracker #1: After every `/compact`, a fake user bubble appeared reading "Compacted (ctrl+o to see full summary)" — text the user never typed.
• Bug Feature/multi session architecture #2: After every `/compact`, chat view got permanently stuck in "thinking" state even though CC was idle.
• Both collapse to one parser bug — the TS + Kotlin transcript watchers were UNWRAPPING ``, letting CC's dimmed echo of its own `/compact` slash-command reach the reducer as a synthetic user-typed message. That message hit `TRANSCRIPT_USER_MESSAGE`'s "no pending match" branch, which both appended a new user bubble AND set `isThinking: true` with no transcript turn to ever clear it.
• Fix moves `` and `` from the unwrap regex to the strip-entirely regex in both parsers.
• UX add: the `compact-summary` transcript event now forwards the actual summary text from the `isCompactSummary` JSONL line. `SystemMarker.tsx` offers a chevron + "view summary" toggle that reveals the CC-produced summary inline — replaces CC's dead "ctrl+o to see full summary" affordance, which never worked inside YouCoded because the chat view consumes that key.
• Added 3 regression tests against the exact CC v2.1.119 JSONL fixture line; existing 946-test suite + tsc both still green.

Root-cause trace

1. `/compact` → `COMPACTION_PENDING` action (spinner card + flag set).
2. CC writes the `isCompactSummary: true` line → `compact-summary` event → `COMPACTION_COMPLETE` → `endTurn()` clears `isThinking` ✓.
3. CC writes a follow-up user-type line: `[2mCompacted (ctrl+o to see full summary)[22m`.
4. Old behavior: `stripSystemTags` unwrapped the tag → "Compacted (ctrl+o to see full summary)" → `user-message` event → reducer fell through to "no pending match" path → fake bubble + `isThinking: true` again.
5. New behavior: `stripSystemTags` strips the tag entirely → empty text → no event → no fake bubble, no thinking flip.

Verified against `~/.claude/projects/.../056880ed-...jsonl:1414`.

Test plan

• `vitest run src/main/transcript-watcher.test.ts` — all 13 pass (3 new)
• `vitest run` (full desktop suite) — 946 pass, 0 fail
• `tsc --noEmit` — clean
• Visual smoke: `/compact` in a dev session, confirm no fake bubble appears, confirm thinking indicator clears, click the "Compacted" marker → summary expands

🤖 Generated with Claude Code