fix(tui): harden terminal resume and runtime context

Summary:
- Keep default auto alternate-screen mode inside the TUI so transcript scrolling stays app-owned unless users explicitly opt out.
- Queue terminal resume events when the engine channel is full, avoiding stranded paused terminal state after interactive tool cancellation or bursts.
- Scope crash-checkpoint recovery to the resolved launch workspace instead of the shell cwd.
- Add runtime deepseek_version to the prompt environment block so agents can distinguish installed runtime identity from a stale checkout.

Test plan:
- cargo test -p deepseek-tui --locked on a simulated merge with current main
- cargo fmt --all -- --check
- git diff --check
- Existing PR CI was green for lint, version drift, Linux/macOS/Windows tests, npm wrapper smoke, and GitGuardian.

config.example.toml

@@ -244,7 +244,7 @@ max_subagents = 10 # optional (1-20)
 # TUI
 # ─────────────────────────────────────────────────────────────────────────────────
 [tui]
-alternate_screen = "auto"   # auto | always | never
+alternate_screen = "auto"   # auto/always use the TUI screen; never uses terminal scrollback
 mouse_capture = true        # true copies only transcript user/assistant text; false uses raw terminal selection/copy
 terminal_probe_timeout_ms = 500 # optional startup terminal-mode timeout (100-5000ms)
 osc8_links = true            # emit OSC 8 escapes around URLs (Cmd+click in iTerm2/Ghostty/Kitty/WezTerm/Terminal.app 13+); set false for terminals that misrender