style: polish investigation workspace

- Summary panel: hide meaningless metrics (questions answered/remaining) until genuinely in progress; remove placeholder timestamps
- Understanding card: increased visual importance via larger heading, lighter border, more padding
- History section: reduced labels to brief forms ('History', 'Situation'), removed uppercase decorative labels from headings
- Investigation Map Preview: lighter borders, muted text, subtle background to signal provisional state
- Turn history cards: removed redundant subheadings ('Your answer', 'What changed') and divider lines
- Button label: 'Update situation' → 'Update'; padding consistent with design tokens
- Condition clarity fix: '!hasSelectedQuestion === false' → 'hasSelectedQuestion'
- Workspace polish section added to UX guidelines

.claude/ux-guidelines.md

@@ -242,3 +242,23 @@ Updated workspace returns
 The interaction is consistent in intent — both modes confirm input acceptance and pause the active response area — but the page-level behaviour differs because one constructs from nothing while the other refines existing context.
 
 Users should never wonder whether their input has been accepted or whether the engine is still reasoning.
+
+## Workspace Polish (v0.7)
+
+The workspace should feel calm. Every visible element must justify its presence.
+
+Unknown values should usually be hidden rather than represented with placeholders.
+
+Whitespace is preferred over decorative UI.
+
+Prefer removing over adding. Prefer consistency over cleverness.
+
+Every section group should feel visually connected — spacing within a group is tighter than between groups.
+
+Labels should be brief. "Investigation History" → "History". "Your response" → "Response". The context already makes the meaning clear.
+
+Headings should be clean. Remove unnecessary subheadings that duplicate context. Remove uppercase labels from headings where they add visual noise without adding information.
+
+Cards should have consistent border radius, padding, and heading treatment across the workspace.
+
+An Investigation Map Preview should look provisional — lighter borders, muted text, subtle background — so the user knows it is a preview rather than completed content.