Drop .cursor rules and npm lockfile; standardize on Bun; remove v1 migration code

- Delete .cursor/rules/boardui.mdc (rules live in AGENTS.md) and
  package-lock.json; README now uses bun install/dev/test/build
- Remove migrateV1Slots, the v1 localStorage key, the legacy "asian"
  cuisine expansion, the ownsPantryStaples fallback, and the pre-BoardUI
  theme-key carryover in the layout init script; drop their tests

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

README.md

@@ -7,14 +7,14 @@ not a misleading "per-serving" number.
 ## Run it
 
 ```bash
-npm install
-npm run dev        # http://localhost:3000 (landing) → /plan (planner)
-npm test           # money math, state validation, meal slots (needs Bun: https://bun.sh)
+bun install
+bun dev            # http://localhost:3000 (landing) → /plan (planner)
+bun test           # money math, state validation, meal slots
 ```
 
-Production: `npm run build && npm start`. Deploys to Vercel as-is (no env vars needed).
+Production: `bun run build && bun start`. Deploys to Vercel as-is (no env vars needed).
 
-Requires Node 20.9+ (Next.js 16).
+Requires Bun (https://bun.sh); Next.js 16 also runs on Node 20.9+ if you prefer.
 
 ## How it works
 
@@ -135,7 +135,7 @@ The big library in `app/lib/recipes/extra/` uses a compact one-entry-per-recipe
 ```
 
 - Each ingredient is `<catalog id> <amount> <unit>`; units: g, oz, lb, ml, tsp, tbsp, cup, each.
-- These all throw when the app loads (and so fail `npm run build`): unknown catalog ids, units that
+- These all throw when the app loads (and so fail `bun run build`): unknown catalog ids, units that
   can't convert to how the item is sold, unknown formats, and duplicate ids.
 - Cups/tbsp on an item sold by weight need `gramsPerMl` on that catalog item.
 - Add the recipe's steps to the matching file in `recipes/steps/`, keyed by its id. The app refuses to