Tier-gated RAG + Drive document sources (#42) (#54)

## Summary

Implements epic [#42](#42) (children #43–#53) and advances [#11](#11).

- **Entitlement:** `allows_rag` on plans (founders / backer / pro / business; not standard); exposed as `features.rag`
- **Gates:** document REST + WS `PromptType.RAG` use `assert_feature_allowed(..., "rag")`
- **Lifecycle:** dedupe ingest, delete vectors by `document_id`, honor `active`, fix document detail PATCH/DELETE
- **Workspaces:** auto-create default company workspace; fail-closed scoping
- **Drive:** personal + company Google/Microsoft connect (`link_drive` / `link_company_drive`), resource selection, sync, webhooks stubs, `sync_drive_connections` management command
- **Docs/env:** README + `.env*.example` updated

Companion FE: `chat_web_app` branch `feature/rag-epic-42-ui` (#81–#85).

## Test plan

- [x] `SKIP_RAG_INIT=1 uv run python manage.py test` (457 OK)
- [ ] Migrate finance `0004` + chat_backend `0028` on beta
- [ ] Verify Standard user: Documents API 403 + no RAG retrieval
- [ ] Verify Founders/Pro: upload + list + active toggle
- [ ] Connect Google/Microsoft Drive (incremental scopes) and Sync
- [ ] Company manager: `link_company_drive`; non-manager 403
- [ ] Run `manage.py sync_drive_connections`Reviewed-on: #54

llm_be/finance/services/plans.py

@@ -41,6 +41,7 @@ PLAN_SEED: list[dict[str, Any]] = [
         "is_selectable": True,
         "allows_text_generation": True,
         "allows_image_generation": True,
+        "allows_rag": True,
         "allows_all_future_features": True,
         "prompt_quota_per_window": 300,
         "prompt_window_hours": 6,
@@ -59,6 +60,7 @@ PLAN_SEED: list[dict[str, Any]] = [
         "is_selectable": False,
         "allows_text_generation": True,
         "allows_image_generation": False,
+        "allows_rag": False,
         "allows_all_future_features": False,
         "prompt_quota_per_window": 100,
         "prompt_window_hours": 6,
@@ -70,13 +72,14 @@ PLAN_SEED: list[dict[str, Any]] = [
         "name": "Pro / Creator",
         "description": (
             "Higher message caps and multi-modal workflows for heavy users, "
-            "including image generation when available."
+            "including image generation and Drive/RAG sync when available."
         ),
         "price_cents": 4000,
         "is_public": False,
         "is_selectable": False,
         "allows_text_generation": True,
         "allows_image_generation": True,
+        "allows_rag": True,
         "allows_all_future_features": False,
         "prompt_quota_per_window": 200,
         "prompt_window_hours": 6,
@@ -87,14 +90,16 @@ PLAN_SEED: list[dict[str, Any]] = [
         "slug": SubscriptionPlan.Slug.BUSINESS,
         "name": "Business Team",
         "description": (
-            "Team seats, centralized auth, priority support, and absolute data "
-            "privacy for local companies handling sensitive data."
+            "Team seats, centralized auth, priority support, company Drive/RAG "
+            "sync, and absolute data privacy for local companies handling "
+            "sensitive data."
         ),
         "price_cents": 9900,
         "is_public": False,
         "is_selectable": False,
         "allows_text_generation": True,
         "allows_image_generation": True,
+        "allows_rag": True,
         "allows_all_future_features": False,
         "prompt_quota_per_window": 300,
         "prompt_window_hours": 6,
@@ -113,6 +118,7 @@ PLAN_SEED: list[dict[str, Any]] = [
         "is_selectable": False,
         "allows_text_generation": True,
         "allows_image_generation": True,
+        "allows_rag": True,
         "allows_all_future_features": True,
         "prompt_quota_per_window": 300,
         "prompt_window_hours": 6,
@@ -415,6 +421,7 @@ def plan_to_dict(plan: SubscriptionPlan | None) -> dict[str, Any] | None:
         "features": {
             "text_generation": plan.allows_feature("text_generation"),
             "image_generation": plan.allows_feature("image_generation"),
+            "rag": plan.allows_feature("rag"),
             "all_future_features": plan.allows_all_future_features,
         },
         "prompt_quota_per_window": plan.prompt_quota_per_window,