fix(web): pin the Claude response viewer to the pane's own conversation

The viewer re-derived a pane's live conversation from the newest
~/.claude/history.jsonl entry for the pane's cwd. A cwd is shared with every
other Codeman tab on it, with tabs long since closed, and with any plain
`claude` the user runs in their own terminal, so the eye followed whichever of
those was typed into last — and since the match was written back through
adoptClaudeSessionId(), the mispin stuck.

Credit a history entry to a pane only when it lands within 10s of that pane's
own Enter and no other pane on the same cwd submitted closer, reusing the
last-submit correlation the Codex locator already relies on. Submit tracking
moves from _codexLastSubmitAt to a mode-agnostic Session.lastSubmitAt. With no
correlated entry the pane keeps the id it has: a viewer one turn behind beats a
viewer showing someone else's conversation.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

test/mocks/mock-session.ts

@@ -19,6 +19,8 @@ export class MockSession extends EventEmitter {
   ralphTracker: null = null;
   writeBuffer: string[] = [];
   terminalBuffer: string = '';
+  /** Mirrors Session.lastSubmitAt — the response viewer credits history entries by it. */
+  lastSubmitAt: number = 0;
 
   private _muxName: string | null = null;