docs(fusion_accounting): per-sub-module CLAUDE.md, UPGRADE_NOTES.md, README.md

Task 20 of Phase 0: document the sub-module split.

- fusion_accounting_core: foundation doc covering security groups, shared-field
  schema preservation, and the Enterprise-detection helper.
- fusion_accounting_ai: preserves the original module's AI-specific design
  decisions, Odoo 19 gotchas, deployment commands, controllers, models, theme
  rules, and known issues. Adds a new Data-adapter pattern section documenting
  tri-mode routing (fusion / enterprise / community).
- fusion_accounting_migration: doc for the Enterprise uninstall safety guard
  and the wizard shell that future feature sub-modules will extend.
- fusion_accounting (meta): rewritten CLAUDE.md as a pure overview pointing at
  sub-modules, plus a new README.md covering one-click install/uninstall.

Each sub-module now has CLAUDE.md (Cursor/Claude context), UPGRADE_NOTES.md
(version-by-version deltas / reference sources), and README.md (user-facing
install/usage docs). 11 files total.

Made-with: Cursor

fusion_accounting_ai/README.md

@@ -0,0 +1,31 @@
+# Fusion Accounting AI
+
+Conversational AI co-pilot for Odoo Accounting using Claude or GPT.
+
+## What it does
+
+Embeds an AI agent in the Odoo Accounting menu. Users chat with the AI, which
+calls into Odoo via tool-functions (read journal entries, find unreconciled
+bank lines, draft follow-ups, generate audit reports, etc.). Tier 3 actions
+(financial writes) require user approval via in-chat approval cards.
+
+## Install profiles
+
+This module works on three install profiles:
+
+1. **Pure Community + this module** — AI uses pure Community searches via the
+   data-adapter `_via_community` paths. Reduced functionality (no rich reports,
+   no Enterprise bank-rec features) but all read tools work.
+2. **Community + this module + fusion native sub-modules** (recommended target) —
+   adapters route to fusion bank rec / fusion reports / etc. Full functionality.
+3. **Community + Enterprise + this module** (legacy) — adapters route to Enterprise
+   APIs. Most functionality available; some Enterprise-specific UI integration
+   (e.g. live cursor in bank-rec widget) not supported.
+
+## Configuration
+
+Settings -> Fusion Accounting AI -> set API keys for Claude (default) and/or OpenAI.
+
+## Troubleshooting
+
+See `CLAUDE.md` in this module for known Odoo 19 gotchas.