Add cross-tool workflow: AGENTS.md, Antigravity workflows, documentation

- Create AGENTS.md (90 lines) as shared foundation for Claude Code + Antigravity
- Slim CLAUDE.md from 113 to 45 lines (Claude-specific only, references AGENTS.md)
- Slim GEMINI.md from 58 to 26 lines (Antigravity-specific only, references AGENTS.md)
- Add 6 Antigravity workflows in .agent/workflows/ (session-start, preflight, token-sync, visual-qa, build-component, page-review)
- Add docs/reference/cross-tool-workflow.md with task routing, quality gates, file ownership, error mitigation
- Zero content overlap between CLAUDE.md and GEMINI.md (was ~80%)
- File ownership boundaries defined for current phase and future backend work

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

.agent/workflows/fa-page-review.md

@@ -0,0 +1,91 @@
+---
+description: Review and tweak an existing page — visual QA, spacing adjustments, copy refinement, responsive check. Current phase focus.
+---
+
+# Page Review
+
+Review an existing page component for visual quality, consistency, and polish.
+This is the primary workflow for the current project phase (tweaking and
+finalising pages rather than building from scratch).
+
+## Arguments
+
+Provide the page name (e.g., `ProvidersStep`, `HomePage`, `CoffinsStep`).
+
+## Steps
+
+### 1. Gather context
+
+- Read the page source: `src/components/pages/{PageName}/{PageName}.tsx`
+- Read its stories: `src/components/pages/{PageName}/{PageName}.stories.tsx`
+- Check `docs/memory/session-log.md` for recent changes to this page
+- Check `docs/memory/decisions-log.md` for relevant design decisions
+
+### 2. Open in Storybook
+
+Navigate to `localhost:6006` and open the page's default story.
+
+### 3. Review checklist
+
+At each breakpoint (375px mobile, 768px tablet, 1280px desktop):
+
+**Visual hierarchy**
+- Heading sizes follow a clear progression (display → h1 → h2 → body)
+- Primary action is visually prominent
+- Whitespace groups related content, separates unrelated
+
+**Spacing**
+- All spacing uses `theme.spacing()` — no magic numbers
+- Consistent gaps between sections (typically spacing(4) or spacing(6))
+- No visual crowding; no excessive empty space
+
+**Typography**
+- Body text line length between 45-75 characters
+- Line heights readable (1.5 for body, tighter for headings)
+- Font weights create clear distinction between labels and content
+
+**Colour**
+- All colours from theme/tokens — no raw hex in source
+- Contrast meets WCAG AA (4.5:1 normal text, 3:1 large text)
+- Error states use copper (#B0610F), not red
+
+**Responsive**
+- Content reflows cleanly between breakpoints
+- No horizontal overflow or content clipping
+- Touch targets at least 44px on mobile
+- Images and cards scale proportionally
+
+**Copy**
+- Warm but not gushy — understated empathy
+- Labels are clear, unambiguous, sentence case
+- CTAs use action verbs ("Continue", "Select", "Save")
+- No jargon or funeral-industry terms without context
+
+**Interactive states**
+- Hover, focus, disabled visible on all controls
+- Focus indicators: 2px solid, 2px offset, visible on `:focus-visible`
+- Disabled: reduced opacity, no pointer events
+
+**Edge cases**
+- Long content handled (truncation, scroll, or wrap)
+- Empty/minimal content doesn't break layout
+- Loading states present where data is async
+
+### 4. Make targeted fixes
+
+For issues found:
+- Make small, focused changes (spacing, copy, alignment)
+- Do NOT restructure the page — this is polish, not redesign
+- Reference design decisions from decisions-log.md when relevant
+
+### 5. Before/after comparison
+
+- Screenshot the page at each breakpoint BEFORE and AFTER changes
+- Present both to the user for approval
+
+### 6. Report
+
+Summarise:
+- Changes made (with file and line references)
+- Remaining issues (with severity P0/P1/P2)
+- Suggested next steps (e.g., "run fa-preflight before committing")