Enhance documentation for UI consistency and field widget layout in README, SPEC, and TASKS

TASKS.md

@@ -11,6 +11,7 @@ Use these rules for every implementation task in this repository:
 - Use `ruff` for linting and formatting.
 - Prefer small vertical slices that can be implemented and verified independently.
 - Keep Proxmox API and business logic out of Textual widgets where possible.
+- Field-like widgets should use compact 3-row layouts by default; bordered fields must not include an empty inner spacer row between the content and the border.
 - Every screen must have explicit default, loading, success, empty, and error states where applicable.
 - Every interactive screen must be covered by Textual interaction tests using `run_test()` and `Pilot`.
 - Important visual states should be covered by snapshot tests.
@@ -26,6 +27,12 @@ Codex should use these commands:
 - Run lint checks: `uv run ruff check .`
 - Format code: `uv run ruff format .`
 
+## Shared visual validation
+
+- Use snapshot tests and visual review for form-heavy screens to confirm that single-line field widgets stay 3 rows high by default.
+- Verify that bordered field-like controls do not render an empty spacer line above or below the value row.
+- Allow taller controls only when a widget is intentionally multi-line or needs additional vertical content, and call that out in the task summary as a UX choice.
+
 ## Implementation backlog
 
 ### Task 1: Bootstrap the Textual app and project structure