fix(shortcuts): add focused editing and host undo/redo in 0.3.13

[lightninglu10]

Fixes editing shortcuts from focused timeline clips and adds host-backed undo/redo in @quantfive/freecut-editor-surface 0.3.13. Delete/Backspace and C are eligible on the exact clip root outside dialogs; C falls back to the sole selected clip at the playhead when nothing is hovered. Editable targets, nested controls, ordinary buttons and dialogs stay protected.

Embedded Cmd/Ctrl+Z and Cmd/Ctrl+Shift+Z call an optional EditorHost.history port. The host owns persistence, serialization and conflict handling, and supplies the resulting snapshot through its existing subscription. Freecut never rewinds its local temporal store in host mode; hosts without the port keep history shortcuts disabled. Standalone local undo remains available. The obsolete broader Z exemption was removed so nested controls and dialogs retain native undo.

Release dependencies: merging this PR into codepress-main allows the existing trusted-publishing workflow to publish 0.3.13. CodePress's durable history backend is in quantfive/codepress#6428; quantfive/codepress#7026 shares its guarded history actions with the new port and prevents double keyboard dispatch. Both are unmerged dependencies. A package upgrade alone does not enable durable history in a host that lacks it. After publication, CodePress can pin 0.3.13, remove only the two original shortcut patch hunks and verify consumer integration. Tracks quantfive/codepress#7001; that issue remains open until adoption.

Validation: 61 focused source tests passed across history, DOM guards, cuts and semantic clip accessibility. Added history regressions failed before the implementation. Six browser cases passed, including real Meta+Z and Control+Z plus Shift+Z redo: deleted clips stay absent until the controlled host emits its undo snapshot, return at their original ranges, and disappear again only after redo adoption. The browser fixture deliberately controls host receipts; these are package integration regressions, not a fresh live CodePress backend QA report. Full type/lint check passed across 2,499 files, and the 0.3.13 tarball builds and passes both installed-consumer tests. Provenance verification also passed during this PR.

The screenshot shows the fixture's deleted clip restored after host undo. Media resolution is disabled in this fixture; playback is not under test.

[codepress-reviewer-dev]

Starting initial review of b6db2679 from baseline b4975a0a... 👀

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