Self-hosting survival: persist chat + CLI session IDs across reloads

[smorchj]

Why

The critical path for using Klonode to edit Klonode. When you edit a server-side file (API route, store, Vite config) while a Claude session is running, Vite restarts the dev server and triggers a full page reload. Before this PR, three things died on that reload:

1. Chat history — chatStore.messages was never persisted. Every reload = empty scrollback.
2. Claude CLI session ID mapping — lived in a component-local `const cliSessionIds: Record<string, string>` inside ChatPanel.svelte. Reset on every remount. Every reload = next message starts a fresh conversation, losing all of Claude's accumulated context.
3. User had no signal — the loading spinner for the in-flight response just vanished, leaving a blank assistant bubble.

With all three lost, self-hosting was unworkable: one typo in a store file or one edit to `api/chat/stream/+server.ts` burned the entire conversation.

What now survives a reload

• Chat history (`klonode-chat` localStorage key, last 80 messages). `chatStore` auto-persists on every update via a subscribe. Transient state (`isLoading`, `error`, `lastComparison`) is left out of the snapshot.
• CLI session ID per tab (`klonode-sessions.cliSessionIds`). Moved from a component-local const into `SessionsState` with `getCliSessionId` / `setCliSessionId` / `clearCliSessionId` helpers exported from `agents.ts`. The next message after a reload resumes the same Claude conversation.
• Per-session message backlog (`sessions.messages`, last 50 per session). The agents API / CO analysis path was already reading from here but it was never persisted. Now it is.
• Date timestamps — rehydration converts ISO strings back to Date objects so `.toISOString()` / formatting code doesn't throw.
• Interrupted flag — any message that was `loading: true` at save time gets `loading: false, interrupted: true` on hydrate. The UI renders a `⚠ response interrupted by reload` banner instead of a spinner that never resolves.

UX additions

• Pulsing amber `● streaming` badge in the chat header while a response is in flight. Tooltip explains that editing a server-side file will interrupt it.
• `⚠ response interrupted by reload` banner on any assistant message that was cut off.

Verified end-to-end with preview

1. Preview server up, page loaded, console clean.
2. Planted 3 messages (user + complete assistant + mid-stream loading) into `chatStore`, and a fake CLI session ID onto the active tab's `cliSessionIds`.
3. Called `location.reload()` — full page reload.
4. Inspected post-reload state:
   • `chatMsgCount: 3` ✓
   • `firstUserMsg: 'Rename getUserById to loadUser'` ✓
   • `cliSessionIdForActive: 'claude-cli-abc-123'` ✓
   • `lastMessage.loading: false, interrupted: true` ✓
   • `isLoading: false` (no stuck spinner) ✓
5. `preview_inspect '.interrupted-banner'` — rendered, amber color (`rgb(251, 191, 36)`), correct text.

No console errors. No regressions in the existing UI.

Storage safety

• `MAX_PERSISTED_CHAT_MESSAGES = 80` and `MAX_PERSISTED_MESSAGES_PER_SESSION = 50` bound the footprint.
• Both `saveState` paths catch `QuotaExceededError` and fall back to persisting session metadata (IDs, active tab, CLI session IDs) without the message backlog. Losing history is cheaper than losing conversation continuity.

Documentation

`docs/self-hosting.md` explains which edit paths are safe during an active chat (`.svelte` files → HMR, everything survives) and which trigger a reload (`.ts` stores, `api/**` routes, Vite config). Includes a safe-vs-risky table, a risky-edit playbook, and pointers to the implementation files for anyone debugging a survival regression later.

Independent of #65

This branch is stacked on main, not on `feat/workstation-self-introspection`. Both PRs are orthogonal and can merge in either order.

Closes

Addresses the self-hosting blocker the original #53 was reaching for. A new tighter tracking issue for the remaining self-hosting work (stream resume across server restarts, worktree-based safer edit paths) can be filed after this lands.