fix: restore full masked refresh on every panel activation

[parsakhaz]

Summary

Reverts the two attempts to lighten the activation refresh (v2.4.11 light repaint, v2.4.14 WebGL keep-alive + atlas clear) and restores the proven v2.4.10 (#308) painting policy: full masked reset+replay on every panel activation, light silent repaint only on pure window refocus. Both lightweight approaches shipped rendering regressions in production; the full refresh is load-bearing for paint correctness.

What each attempt broke

• v2.4.11 (light repaint on activation): stale frames from the hide→show renderer swap survived as ghosted/overdrawn rows persisting through live output.
• v2.4.14 (keep-alive contexts + clearTextureAtlas on attach): xterm terminals with the same font/theme share one texture atlas — clearing it from one terminal poisoned every other live terminal's glyph cache. Symptom: garbage glyphs that self-repair only where text is selected (selection re-rasterizes those cells with new colors → fresh atlas entries).

What is kept from the perf work

• Single replay per activation (not the old ×2 with the 300ms duplicate)
• 512KiB getState cap and no 8MB serialized-snapshot tag-along — bounds each replay
• Baked light palette (no per-frame GPU invert filter), contrast floor
• Serialize-on-hide throttle, blur-gated animations, hidden-container fit guards

Code changes

• needsFullActivationRefreshRef back to useRef(true), re-armed on every panel hide (and battery saver), consumed on execution — i.e. fix: repaint terminal panels on window refocus (#306) #308's exact depth policy
• Removed panelActivationRef/showMask split (mask == full refresh again)
• Revert of fix: keep WebGL contexts across panel hides to stop renderer-swap ghosting #313 (keep-alive + atlas clear); dispose-on-hide restored, deferred post-attach refresh kept, no clearTextureAtlas
• Lifecycle JSDoc rewritten to document the shared-atlas hazard and mark the activation refresh as do-not-remove without an offline renderer-swap repro

Pre-Merge Testing

• Switch tabs/panes with streaming Claude/Codex TUIs — no ghosted rows, no garbage glyphs, no manual Refresh needed (brief refresh mask on each switch is expected and intended)
• Select text in a busy terminal — renders correctly before and after
• Blur 15s → refocus — clean repaint
• Battery saver re-sync unchanged

Build Verification

• pnpm typecheck passes
• pnpm lint passes (0 errors)