feat: add dot.trackWhileParked — dot follows the live point while scrolled back

[ianlapham]

What

• Opt-in dot.trackWhileParked on LiveChart (default false): while scrolled back or overscrolled, the live dot tracks the true live point's x and keeps its heartbeat pulse, instead of pinning to the plot's right edge with the pulse suppressed.
• The dot hides once the live point leaves the visible window; most visible with timeScroll.overscroll (drag into blank future space and the dot detaches from the edge, pulsing at the real last price). Time scroll demo gains a Dot tracks live point switch; guide + API docs updated.

Why the flag exempts the dot from hideLiveOnScrollBack

• The default hide exists because the edge-pinned dot marks an off-screen price while parked; a tracking dot marks the honest live position, so hiding it would make the flag a no-op under the default timeScroll.
• Only the dot is exempt — the badge and value line keep the default scroll-back hide, and the dot still self-hides once the live point leaves the window.

Why badge.followViewEdge wins

• An edge-pinned followViewEdge dot must stay aligned with its badge, so the flag (tracking, pulse, and hide exemption) is ignored when both are set — documented in the JSDoc and guide.

Test plan

• npm run verify green; coverage thresholds hold (branches 90, functions/lines/statements 95).
• New tests: resolveDot defaults/overrides, useLiveDot parked x math (tracked position, out-of-window both sides, empty data, degenerate window/plot width, live-follow pin, followViewEdge precedence), DotOverlay pulse-while-parked render, LiveChart render for both flag states + precedence.
• The pulse derived values are UI-thread worklets Jest's stub doesn't execute (same as the existing suppression tests) — exercised in the Expo demo app instead. The equivalent behavior has been running in production at FOMO for a few weeks.

🤖 Generated with Claude Code

[brandtnewlabs]

Resolved the merge blocker by merging current main and reconciling all Unreleased changelog entries. The source, tests, docs, and demos merged cleanly; no implementation defect was found in the PR.

Review and QA completed:

• Public API JSDoc, API reference, time-scroll guide, changelog, and interactive example-app control are present.
• npm run verify passed: typecheck, lint, 99 test suites; 1,522 tests passed and 5 skipped.
• React Doctor: 96/100 with no issues.
• iPhone 17 Pro agent-device QA verified tracked-dot positioning and pulse while overscrolled, followViewEdge precedence, and hiding once the live point leaves the visible window.

Fix commit: 88bdf3b. The refreshed branch is ready to merge once its new-head checks finish.