feat(ui): import comprehensive UX system from beads

Import beads' UX design system into gastown:

- Add internal/ui/ package with Ayu theme colors and semantic styling
  - styles.go: AdaptiveColor definitions for light/dark mode
  - terminal.go: TTY detection, NO_COLOR/CLICOLOR support
  - markdown.go: Glamour rendering with agent mode bypass
  - pager.go: Smart paging with GT_PAGER support

- Add colorized help output (internal/cmd/help.go)
  - Group headers in accent color
  - Command names styled for scannability
  - Flag types and defaults muted

- Add gt thanks command (internal/cmd/thanks.go)
  - Contributor display with same logic as bd thanks
  - Styled with Ayu theme colors

- Update gt doctor to match bd doctor UX
  - Category grouping (Core, Infrastructure, Rig, Patrol, etc.)
  - Semantic icons (✓ ⚠ ✖) with Ayu colors
  - Tree connectors for detail lines
  - Summary line with pass/warn/fail counts
  - Warnings section at end with numbered issues

- Migrate existing styles to use ui package
  - internal/style/style.go uses ui.ColorPass etc.
  - internal/tui/feed/styles.go uses ui package colors

Co-Authored-By: SageOx <ox@sageox.ai>

internal/doctor/hook_check.go

@@ -32,6 +32,7 @@ func NewHookAttachmentValidCheck() *HookAttachmentValidCheck {
 			BaseCheck: BaseCheck{
 				CheckName:        "hook-attachment-valid",
 				CheckDescription: "Verify attached molecules exist and are not closed",
+				CheckCategory:    CategoryHooks,
 			},
 		},
 	}
@@ -207,6 +208,7 @@ func NewHookSingletonCheck() *HookSingletonCheck {
 			BaseCheck: BaseCheck{
 				CheckName:        "hook-singleton",
 				CheckDescription: "Ensure each agent has at most one handoff bead",
+				CheckCategory:    CategoryHooks,
 			},
 		},
 	}
@@ -346,6 +348,7 @@ func NewOrphanedAttachmentsCheck() *OrphanedAttachmentsCheck {
 		BaseCheck: BaseCheck{
 			CheckName:        "orphaned-attachments",
 			CheckDescription: "Detect handoff beads for non-existent agents",
+			CheckCategory:    CategoryHooks,
 		},
 	}
 }