feat: UX behavioral foundations — Krug's usability principles as shared design infrastructure

Add UX_PRINCIPLES resolver distilling Steve Krug's "Don't Make Me Think" into
actionable guidance for AI agents. Injected into all 4 design skills as a shared
behavioral foundation complementing the existing visual checklist (WHAT to check)
and cognitive patterns (HOW designers see) with HOW USERS ACTUALLY BEHAVE.

Methodology rewire: 6 Krug usability tests woven into existing design-review
phases — Trunk Test, 3-Second Scan, Page Area Test, Happy Talk Detection with
word count metric, Mindless Choice Audit, Goodwill Reservoir tracking with
visual dashboard. First-person narration mode for design-review output with
anti-slop guardrail.

Hard rules: 4 Krug always/never rules in DESIGN_HARD_RULES (placeholder-as-label,
floating headings, visited link distinction, minimum type size). Krug, Redish,
Jarrett added to plan-design-review references.

Token ceiling: gen-skill-docs.ts warns if any SKILL.md exceeds 100KB (~25K tokens).
Documented in CLAUDE.md.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -138,6 +138,11 @@ SKILL.md files are **generated** from `.tmpl` templates. To update docs:
 To add a new browse command: add it to `browse/src/commands.ts` and rebuild.
 To add a snapshot flag: add it to `SNAPSHOT_FLAGS` in `browse/src/snapshot.ts` and rebuild.
 
+**Token ceiling:** Generated SKILL.md files must stay under 100KB (~25K tokens).
+`gen-skill-docs` warns if any file exceeds this. If a skill template grows past the
+ceiling, consider extracting optional sections into separate resolvers that only
+inject when relevant, or making verbose evaluation rubrics more concise.
+
 **Merge conflicts on SKILL.md files:** NEVER resolve conflicts on generated SKILL.md
 files by accepting either side. Instead: (1) resolve conflicts on the `.tmpl` templates
 and `scripts/gen-skill-docs.ts` (the sources of truth), (2) run `bun run gen:skill-docs`