refactor(runtime): migrate detail-panel surfaces to context components (#1237)

[gfargo]

What

Fourth surface-migration batch (after #1295) — the detail/inspector cluster. The ten per-view detail surfaces now mount as context-reading components: renderDetailPanel returns h(<Surface>Component, props) instead of calling the positional renderer inline.

• Eight preview/context panels (commit, compose-context, branch/tag/stash/submodule previews, issue + PR triage previews) share one positional signature → grouped under a keyed cache.
• Commit-sourced diff detail and the history inspector take their async slices as component props (detail/loading; +filePreview/filePreviewLoading/tabbed for the inspector).

Behavior-preserving

The detail renderers keep their positional signatures and colocated render-snapshot suites unchanged — focused is derived inside each wrapper from state.focus === 'detail', exactly as the dispatcher did, so output is identical. renderDetailPanel gains a leading React param and no longer destructures context/contextStatus (the components self-serve those). The transient overlays (help/palette/pickers/confirmation/chord) stay positional — a separate concern.

Tests

• New detailPanel.test.ts pins view→component routing + prop threading (without a renderer).
• singlePane.test.ts updated to render the inspector through the context shim (the header.test.ts Proxy pattern), still asserting full-width (80) in single-pane.
• overlays.test.ts gets the new React arg — its overlay branch returns before any component, so it's otherwise unaffected.

Validation

tsc clean · full jest green (3611 passed, 68 snapshots; 4 tsTreeSitterParser .wasm-backed failures = known worktree gotcha, pass in CI) · eslint 0 errors · rollup -c builds.

Next

PR 6 (final): per-surface memoization + prune the now-dead threading in app.ts (SurfaceRenderContext / MainPanelExtras shrink to true per-surface slices), then close #1237. Ladder in specs/surface-context-migration-plan.md.