feat(history): restore responsive selector header and sidebar-aware margin

[Alan-TheGentleman]

Closes #1479

Summary

• Restores @carolitascl's responsive selector header and sidebar-aware overlay margin (split out of feat(history): GC/compaction with active-writer and failure-path tests (slice 6/6) #1394 in e2cca1f9b), adapted to the current selector structure. Co-authored in the commit.
• The sidebar now publishes its rail width through SidebarState.railColumns instead of a hardcoded constant; a missing or invalid value falls back to the previous full-width behavior.

Changes

File	Change
extensions/history/index.ts	Three-mode header layout, compact list rows, live overlay margin, wheel band per layout.
extensions/history/selector-helpers.ts	planHeaderLayout, scope radio text, editorOverlayMargin reading railColumns.
lib/shell-sidebar.ts, lib/shell-sidebar-layout.ts	SidebarState.railColumns, set by installSidebar.
docs/prompt-history.md	New "Selector layout" section.
tests/…	Contributor's header and margin suites restored and adapted, plus rendered-layout and real sidebar seam coverage.

Test plan

• node --experimental-strip-types --test tests/*.test.ts → 3848 pass, 0 fail, 43 skipped.
• node scripts/check-types.mjs → no regressions against the recorded baseline.
• Native review approved.

Summary by CodeRabbit

• New Features
  • The history selector now adapts its header to terminal width, stacking or abbreviating controls when space is limited.
  • The selector stays within the editor column when a fullscreen sidebar is visible and adjusts as the sidebar width changes.
  • The selector maintains a consistent 30-row height across layouts.
• Documentation
  • Added guidance on responsive layouts and sidebar-aware positioning.

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Run ID: d4c234bb-2756-4e8d-a96c-f73ced770322

📥 Commits

Reviewing files that changed from the base of the PR and between 5167c5c and 4c89734.

📒 Files selected for processing (11)

• docs/prompt-history.md
• extensions/history/index.ts
• extensions/history/selector-helpers.ts
• lib/shell-sidebar-layout.ts
• lib/shell-sidebar.ts
• odd/tasks/history-followups.md
• tests/history-header-layout.test.ts
• tests/history-lazy-windowing.test.ts
• tests/history-openflow-integration.test.ts
• tests/history-overlay-margin.test.ts
• tests/history-wheel-mouse.test.ts

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