Resolve four mypy contract violations with source-level typing fixes

Resolve four mypy contract violations with source-level typing fixes

Summary

Fixed the reported mypy errors by tightening type contracts at their source:

1. editor.py: added explicit Rich style narrowing so Text.stylize() always receives StyleType.
2. web_fetch.py: marked _handle_http_error() as NoReturn because it always raises.
3. compaction/types.py: made compaction status constants literal-typed (Final[Literal[...]]) and defined CompactionStatus as a type alias.
4. shell_runner.py: unpacked render_bash() tool render tuple and returned only the renderable content as required by RenderableType.

No shims, no fallback branches, and no cast-based suppression were introduced.

Files changed

• src/tunacode/ui/widgets/editor.py
• src/tunacode/tools/web_fetch.py
• src/tunacode/core/compaction/types.py
• src/tunacode/ui/shell_runner.py

Verification

• uv run mypy src/tunacode/ui/widgets/editor.py src/tunacode/tools/web_fetch.py src/tunacode/core/compaction/controller.py src/tunacode/ui/shell_runner.py src/tunacode/core/compaction/types.py ✅
• uv run ruff check src/tunacode/ui/widgets/editor.py src/tunacode/tools/web_fetch.py src/tunacode/core/compaction/types.py src/tunacode/ui/shell_runner.py ✅