feat!: remove the legacy Timeline

[lukecotter]

📝 PR Overview

Removes the legacy Timeline. The pixi.js flame chart replaced the canvas 2D chart in 1.20.0, which stayed behind lana.timeline.legacy as a temporary fallback — its own description said it would go in a future release. 1.22 deprecates it; this drops it.

Targets 1.24, the removal release. Draft until then.

🛠️ Changes made

• Delete the legacy renderer (features/timeline/services/Timeline.ts), its <timeline-legacy> host, and the test that covered only its find listeners.
• Delete the lana.timeline.legacy and lana.timeline.colors settings from the schema, Config and LanaSettings.
• Drop the two-renderer branching in TimelineView: the renderer choice, the palette fork, and the two toolbar buttons legacy used to hide. The skeleton still waits for settings, now on a settingsReady flag.
• With one renderer left, a legend chip always stands for one category, so TimelineKeyEntry holds a category instead of a label plus a group of them. That retires the category folding in toTimelineKeys and the comma-joined data-category.
• Remove the legacy colours section and the revert tip from the docs site, plus the screenshot only that section used.
• Add a second ## [Unreleased] section for 1.24, above the one that ships as 1.22. Deliberate: it keeps this entry off the lines the version stamp will touch. The two collapse into one when 1.22 is tagged.

🧩 Type of change (check all applicable)

• 🐛 Bug fix - something not working as expected
• ✨ New feature – adds new functionality
• ♻️ Refactor - internal changes with no user impact
• ⚡ Performance Improvement
• 📝 Documentation - README or documentation site changes
• 🔧 Chore - dev tooling, CI, config
• 💥 Breaking change

📷 Screenshots / gifs / video [optional]

No visual change to the Timeline. The Settings pane loses two entries under Apex Log Analyzer → Timeline.

🔗 Related Issues

related #

✅ Tests added?

• 👍 yes
• 🙅 no, not needed
• 🙋 no, I need help

A removal. The legacy-only suites are deleted; the rest are rewritten onto the one-category legend shape. pnpm test: 187 suites, 2610 tests, all pass. pnpm lint: 0 errors. pnpm build: clean.

📚 Docs updated?

• 🔖 README.md — never mentioned the legacy timeline
• 🔖 CHANGELOG.md
• 📖 help site
• 🧪 Marked any pre-release-only features
• 🙅 not needed

Anything else we need to know? [optional]

Two open questions for you, neither blocking:

1. No deprecation path. Anyone who set lana.timeline.legacy or lana.timeline.colors keeps a dead key in settings.json, which VS Code flags as an unknown setting. A deprecationMessage on both keys for one release would soften that — one property each in package.json if you want it.
2. The settings shape is hand-kept in three places — the package.json schema, Config in lana/, and LanaSettings in log-viewer/. Removing one boolean meant editing all three, and nothing would have caught a miss. Worth a parity test, but not in a removal PR.