refactor: codebase review cleanup — dead code, duplication, complexity, unified patterns

[stefanhoelzl]

Fixes from a review of the codebase for unused code, overly complex code, duplication and patterns worth unifying. Squashed from the review branch and merged with main's concurrent-hooks / single-writer-fold changes.

Bugs

• POSIX CWD-release cleanup shares one runner (cwd-release-kill.ts) with Windows: errors and surviving processes are reported to the deletion instead of swallowed by a bare catch {}
• Timeouts always clear their timer (raceTimeout / withTimeout in src/utils/timeout.ts): dialog sessions, ProcessRunner.wait, OpenCode connect, the dialog mock
• .cmd shims quote every argument (runAgentBinary, OpenCode launcher; shared cmd-quote.ts)
• appctrl expand-sidebar retries like the e2e fixture (one shared expandSidebarOn)
• DialogView walls off its form with an ErrorBoundary like PanelView; Form's orphan-focus timer is cleared on unmount
• delete pipeline reports the kill-blockers step when the removal fails
• CLAUDE.md rule violations: node:fs stat in api-server, string paths, path log-context keys, direct process.platform; ElectronBuildInfo's sync git call documented as an exception

Interface changes

• ApiResult (with category) declared once in shared/api-protocol.ts
• one workspace-identity shape (workspaceIdentityPayloadSchema) in workspace event payloads; agent:status-updated flattened
• workspace:open decides fresh-vs-reopen once: fresh + workspaceName on every hook context and on workspace:created (plugin stdin keeps reopened)
• streaming yield frames validated against per-hook-point frames schemas
• UiState row keys are workspace refs; the agent runtime is keyed by WorkspaceRef
• modules declare handlers with defineHooks / defineEvents (src/intents/declarations.ts): ~170 event as / ctx as / intent as casts removed, mistyped handlers fail to compile
• every operation resolves workspaces through resolveWorkspaceIdentity

Simplification and deduplication

• presentation module split into startup-surface / running-hooks / navigation / view-model (2,622 → ~1,630 lines); creation FormState
• claude handleHook status rules extracted into a pure deriveStatus reducer with focused tests
• delete pipeline state object, idempotency (singleton = per-key with a constant key; main's wait kept), open-project, app-start retry, git-worktree identify, ide-server lifecycle, api-server socket handling
• plugin module binds hook points from OPEN_WORKSPACE_HOOKS / DELETE_WORKSPACE_HOOKS; hooks and automations share one script runner
• sidekick extension split into connection / agent-terminal / ui-handlers / codehydra-api / workspace-commands
• shared helpers: tagKey/encodeTag, prependPath, errorCode/toError, streamDownloadProgress, escapeHtml, FieldShell, .ch-icon-button, status cache with (ref, previous, next) transitions, activeWorkspaceRef
• dead code removed: global dialog CSS, unused mock factories, test-only guards, storeText, unused deps ignore and @testing-library/user-event
• test setup deduplicated (~3.4k lines; no test removed)
• docs: PATTERNS.md error-surfacing rule, accurate shutdown-handler rule, stale references fixed

Left alone on purpose: extensions/markdown-review-editor/, migration code.