feat: Gemini CLI E2E tests (v0.9.2.0) (#252)

* feat: add Gemini CLI session runner + JSONL parser

Subprocess wrapper for `gemini -p --output-format stream-json --yolo`
that spawns the Gemini CLI and parses NDJSON events (init, message,
tool_use, tool_result, result) into a structured GeminiResult.

Includes 10 unit tests for parseGeminiJSONL covering happy path,
malformed input, empty input, missing fields, and multi-tool scenarios.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat: add Gemini CLI E2E tests

Two E2E tests (gemini-discover-skill, gemini-review-findings) that
verify gstack skills work when invoked by the Gemini CLI. Follows
the same pattern as codex-e2e.test.ts — gated by EVALS=1 + binary
availability, diff-based selection via touchfiles, eval persistence.

- Add test/gemini-e2e.test.ts
- Add Gemini entries to E2E_TOUCHFILES and GLOBAL_TOUCHFILES
- Add test:gemini and test:gemini:all scripts to package.json
- Add gemini-e2e.test.ts to test:evals, test:e2e, and ignore list

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* chore: bump version and changelog (v0.9.2.0)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

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Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>