test(server): wait for PTY readiness conditions

[danyaberezun]

Summary

• Replace elapsed-time assumptions in terminal replay and natural-exit tests with observed PTY output/exit readiness.
• Reproduce and cover the slow-login-shell race without changing production terminal behavior or APIs.

Closes #290

Changes

• Add a bounded, history-aware waiter around the existing injected terminal publisher.
• Match output across all terminal.data batches for the expected terminal id and wait for the matching terminal.exit before reattach/persistence assertions.
• Build marker commands so their expected output is not present contiguously in echoed input, preventing PTY echo from impersonating command execution.
• Migrate the two reported replay cases, the reported natural-exit case, and its restart-survival duplicate; document the invariant in the terminal module spec.
• Leave unrelated busy-process and ownership test timers out of scope.

Testing

• bun run check:deps — passed.
• bun run check:seams — passed.
• bun run lint — passed with six pre-existing unused-suppression warnings outside this diff.
• bun run typecheck — 11/11 tasks passed.
• bun run test — 11/11 tasks passed; server 846/846 tests passed.
• SHELL=/usr/bin/bash bun test packages/server/src/terminal/terminalManager.test.ts --rerun-each=3 — 78/78 passed.
• SHELL=/usr/bin/zsh bun test packages/server/src/terminal/terminalManager.test.ts --rerun-each=5 — 130/130 passed under concurrent verification load.
• Four target cases with an injected two-second zsh startup delay, --rerun-each=3 — 12/12 passed.
• An 18-second startup-delay probe failed at the bounded 15-second deadline with the missing condition and terminal id.
• bun run e2e — 298/298 passed before the final timeout-only hardening commit; not rerun on the final head locally, with current-head coverage left to CI.

[jetbrains-air]

Approved — ready to merge.

[jetbrains-air]

Approved — ready to merge.

[jetbrains-air]

Approved — ready to merge.

[jetbrains-air]

Approved — ready to merge.