Harden keybinding parsing, modes/conflicts, and chord coverage

[RtlZeroMemory]

Summary

This PR hardens the existing keybinding system without adding new syntax/features. It audits and tightens parsing, chord/mode behavior, and conflict resolution, then adds deterministic regression coverage and updates docs.

Fixes

• Reject duplicate modifiers in key strings (e.g. ctrl+ctrl+a).
• Make same-sequence re-registration replace the prior binding in mode registration flows.
• Make setMode() throw for unknown/unregistered modes (clear error).
• Preserve handler-driven mode changes during app key routing so they apply to subsequent events.

Tests Added

New deterministic suites under packages/core/src/keybindings/__tests__/:

• keybinding.parse.test.ts
• keybinding.chord.test.ts
• keybinding.modes.test.ts
• keybinding.conflicts.test.ts
• keybinding.mode-switch.test.ts

The new suites cover parser edge cases, chord matching/timeout semantics, mode inheritance/switching, routing/conflict precedence, and integration behavior around handler-triggered mode switches.

Documentation

• Updated docs/guide/input-and-focus.md with a consolidated Keybinding System section documenting syntax, chord behavior, mode rules, conflict resolution, and routing order.

Validation

• npm run lint
• npm run build
• npm run typecheck
• node scripts/run-tests.mjs

All commands pass on this branch.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Propagate keybinding handler failures before consuming input

This routing path applies keyResult.nextState and consumes the event without checking keyResult.handlerError, so handler exceptions are silently dropped in app runtime. That became user-visible in this commit because setMode() now throws for unknown modes: a typo like app.setMode("inert") inside a keybinding handler is swallowed here, the key is still treated as consumed, and no fatal/error is surfaced, making mode bugs hard to diagnose.

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[RtlZeroMemory]

Fixed in 220d04c.

createApp now checks keyResult.handlerError after keybinding routing (for both raw key events and synthetic key events from text input), enqueues ZRUI_USER_CODE_THROW, and stops processing the batch.

Added regression test: unknown mode switch inside keybinding handler surfaces fatal error in packages/core/src/keybindings/__tests__/keybinding.mode-switch.test.ts.