feat(#256): add complete chart style presets

[BorisTyshkevich]

What & why

Closes #256.

Extend the existing Line/Area Style selector to seven complete presentation presets while keeping advanced Spec combinations lossless and visible as disabled Custom. Add exact pure preset matching/application, renderer semantics for scale/legend/grid/axes, canonical schema/completion support, and persistence coverage across saved/shared/Dashboard flows.

Verification

• npm test — 101 files, 2,813 tests passed; coverage gate passed
• npm run build — generated-schema check passed; dist/sql.html built
• npm run test:e2e — 115 passed on the initial matrix; five unrelated Firefox navigation/setup timeouts passed 5/5 with npx playwright test --last-failed
• independent read-only code review — no actionable findings

Checklist

• npm test passes (the per-file coverage gate is non-negotiable)
• Tests added/updated in the same change as the code
• npm run build succeeds (single-file dist/sql.html)
• Layers kept honest: pure logic in src/core/, network in src/net/ (injected fetch), DOM in src/ui/
• No new runtime dependency (or it's a deliberate, justified addition — see CONTRIBUTING)
• README / CHANGELOG.md ([Unreleased]) updated if behavior or the deployed surface changed
• Reconciled affected tracked work (roadmap Roadmap to 1.0.0 #68, the issue body, ADR/CHANGELOG) if this change reshaped it