Add opt-in live session indicators and unread result markers

[priva7eer]

Summary

The chat list currently gives no indication that an agent is working or that a completed result is waiting to be read. Add codexExtras.showSessionStatusIcons, an experimental setting that is off by default, so the author's existing icons and metadata-only reads remain unchanged unless enabled.

• Blue spinner for confirmed live work, yellow bell for blocking input/approval waits, and yellow question mark for unanswered non-blocking questions.
• Green check for a new result. Opening it successfully through Extras acknowledges that specific result across reloads; failed opens and stale clicks cannot acknowledge a newer completion.
• Orange interrupted and red failed indicators. Small gray dots for idle, unknown, and reviewed states keep text aligned. Unconfirmed activity uses a muted clock, never a spinner inferred from an unfinished log.
• Match async answers individually, including legacy rehydrated IDs; expire superseded and abandoned questions.

Uses file events and a read-only local IPC observer rather than status polling. The observer sends no task-control requests and retains runtime state and pending question IDs, not transcripts. Log reads are cached and limited to the final 256 KiB. The setting toggles without reloading.

Compatibility: the IPC stream is internal and undocumented (verified with openai.chatgpt 26.1007.21434 on Windows). Disconnects, unsupported stream versions, and revision gaps invalidate or reconcile live state. A connected but frozen owner cannot be reliably detected. Unix endpoint support is implemented and covered by mocked transport tests; live Unix connectivity has not been verified. Details: docs/SESSION-STATUS.md.

Independent of #13; archive changes are excluded. No version bump, dependencies, or generated VSIX files.

Closes #14

Validation

• Windows, Node 24.14.0: npm ci --offline --no-audit --no-fund, npm test (41/41), and npm run package -- --out codex-extras-status.vsix.
• Ubuntu via WSL, Node 22.23.3: npm test (41/41) and npm run package -- --out codex-extras-status-ci.vsix. Dependencies installed from the npm cache with --offline --ignore-scripts --no-audit --no-fund because DNS was unavailable.
• Regression coverage includes IPC framing and disconnection, protocol/revision mismatches, bounded log reads, option toggling, question reconciliation, persistent result acknowledgement, failed opens, and completion/open races.
• Manual Windows smoke testing during development: local IPC handshake and runtime snapshots, working state, question-state corrections on existing sessions, local VSIX installation, and result-review indicators. The final neutral-dot visual still requires a window reload for visual confirmation.
• git diff --check passes; README and changelog updated.

Checklist

• The change is focused and contains no unrelated files.
• npm test passes.
• npm run package succeeds.
• User-facing behavior is documented.
• CHANGELOG.md is updated when appropriate.
• No credentials, personal data, or generated build artifacts are committed.