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>

GEMINI.md

@@ -1,58 +1,26 @@
-# FA 2.0 Design System — Antigravity Rules
+# Antigravity — FA 2.0 Design System
 
-## Project context
+Follow all rules in `AGENTS.md`. This file contains Antigravity-specific behaviour only.
 
-Funeral Arranger (funeralarranger.com.au) design system rebuild. Parsons is the
-client. The design language must be warm, professional, trustworthy, and calm.
-Users are often in distress.
-
-## Tech stack
-
-- React 18 + TypeScript
-- Material UI (MUI) v5
-- Storybook 8+ (running on localhost:6006)
-- Style Dictionary for token transformation
-- W3C DTCG token format
-
-## Hard rules
-
-1. **Never hardcode colours, spacing, typography, or shadows** — always consume the MUI theme (`theme.palette.*`, `theme.spacing()`, `theme.typography.*`) or CSS custom properties (`var(--fa-*)`)
-2. **Never use raw hex values in components** — map to semantic tokens
-3. **Follow atomic design tiers:** atoms → molecules → organisms → templates → pages
-4. **Component folders:** PascalCase, each contains `ComponentName.tsx`, `ComponentName.stories.tsx`, `index.ts`
-5. **Token files:** camelCase in `tokens/` directory (primitives → semantic → component tiers)
-6. **CSS custom properties prefix:** `--fa-`
-7. **Error styling uses copper (#B0610F)** not red — this is intentional for grief-sensitive context
-8. **Copy tone:** warm but not gushy. Understated empathy. Let UI structure be the empathy.
-
-## Token access convention
-
-- Semantic tokens: `theme.palette.*`, `theme.typography.*`, `theme.spacing()`
-- Component tokens: `var(--fa-component-property-state)`
-- Never mix — semantic via theme, component via CSS vars
-
-## Storybook
-
-Dev server runs on `localhost:6006`. When verifying components visually, navigate
-to the specific story URL. Story IDs follow the pattern:
-`/story/{tier}-{componentname}--{variantname}`
-
-## File structure
-
-```
-src/components/atoms/       — Button, Input, Typography, Card, etc.
-src/components/molecules/   — SearchBar, PriceCard, ServiceOption, etc.
-src/components/organisms/   — Navigation, Footer, ArrangementDialog, etc.
-src/components/templates/   — WizardLayout
-src/components/pages/       — IntroStep, ProvidersStep, etc. (wizard steps)
-tokens/primitives/          — Raw values (hex, px, font names)
-tokens/semantic/            — Design intent (color.text.primary)
-tokens/component/           — Per-component tokens
-```
-
-## When making visual changes
+## Visual verification
 
+When reviewing or making visual changes:
 1. Make the code change
-2. Open the Storybook story in the browser to verify
+2. Open the Storybook story in the browser at `localhost:6006`
 3. Screenshot and check spacing, alignment, visual weight
 4. Self-correct if something looks off before presenting
+
+Story URL pattern: `/story/{tier}-{componentname}--{variantname}`
+
+## Cross-tool workflow
+
+This project uses both Claude Code and Google Antigravity.
+See `docs/reference/cross-tool-workflow.md` for task routing and coordination.
+
+Antigravity owns: visual QA, browser verification, page-level review screenshots.
+Claude Code owns: component building, token creation, code quality, memory updates, git.
+
+## Workflows
+
+Custom workflows available in `.agent/workflows/`:
+`fa-session-start`, `fa-preflight`, `fa-token-sync`, `fa-visual-qa`, `fa-build-component`, `fa-page-review`