Keep the dev window alive during UI reloads

[lastobelus]

Part of #196.

This is slice 1 of the approved stack. Slice 2, the shared element picker and highlighter, will be based on this PR.

What changes

• Builds renderer, preload, startup, HTML, CSS, and brand assets into an atomic worktree-local live directory.
• Reloads that renderer inside the existing Electron process and BrowserWindow, preserving native window geometry and focus.
• Leaves the last working UI visible when a renderer build fails.
• Reports main-process or backend edits as restart-required without closing the app.
• Freezes and flushes mutable review state before reload so in-progress edits are not lost.
• Lets a replacement watcher attach to the existing live instance; Ctrl-C still performs managed shutdown.
• Keeps startup mode armed after an initial build failure, so the next valid edit performs the full launch instead of trying to reload a missing process.

Done when

• Renderer edits reload in the existing process/window.
• Failed renderer builds preserve the last published UI.
• Runtime edits do not restart the app automatically.
• Review edits, attachments, autosave, and workspace state cross the reload durability barrier.
• Automated gates pass and native PID/geometry/focus QA proves the same window survives.

Excludes

• The element picker/highlighter (slice 2).
• Hot-swapping Electron main-process or backend code.
• Preserving arbitrary renderer in-memory state.
• Visual changes from Improve Markover review UI #195.
• Compatibility paths for unreleased prototype behavior.

Validation

• Build, lint, typecheck, notices: pass.
• Focused live-reload/durability/service tests: 71/71 pass.
• Smoke: pass.
• Full suite: 829/830; the existing order-sensitive remote-creation-journal concurrency assertion observed the same two valid digests in reverse order. Its focused file passes 7/7.
• Native QA: successful CSS reload, deliberate renderer build failure, recovery reload, and QA cleanup all retained PID 33981, native window 14598, and bounds 1180x760 @ (145,34). LastCode remained frontmost throughout.

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