Phase 0: backend + frontend scaffold, single-binary build

Implements the Pansy v1 scaffold (epic #20, phase 0).

#1 Backend: Go module (pure-Go, builds with CGO_ENABLED=0), env config,
   gin server with slog + recovery + /api/v1/healthz, modernc SQLite store
   with WAL/busy_timeout/foreign_keys pragmas, embedded numbered-migration
   runner, full initial schema (users, sessions, gardens, garden_shares,
   garden_objects, plants, plantings), domain structs + sentinel errors,
   graceful shutdown.

#2 Frontend: Vite + React 19 + TS (strict) + Tailwind 4 + TanStack
   Router/Query, typed /api/v1 fetch wrapper (ApiError carries status +
   body so later issues can read 409 conflict rows), dev proxy /api -> :8080,
   responsive app shell with stub pages for all five routes.

#3 Single binary: //go:embed of the web build with a committed placeholder,
   SPA fallback (deep links, immutable asset caching, JSON 404 for unmatched
   /api and missing assets), Makefile (web/build/dev/test), README quickstart
   + env var table.

Verified: go build/vet/test clean (CGO off); binary migrates idempotently and
serves healthz; web tsc + build clean; integrated binary serves the SPA, deep
links, and correct cache headers; app mounts and navigates all five routes at
desktop and 375px widths.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_01JdQpdYYsTgtkJBxbcpAszi

web/tsconfig.json

@@ -0,0 +1,29 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "useDefineForClassFields": true,
+    "lib": ["ES2022", "DOM", "DOM.Iterable"],
+    "module": "ESNext",
+    "skipLibCheck": true,
+
+    "moduleResolution": "bundler",
+    "allowImportingTsExtensions": true,
+    "resolveJsonModule": true,
+    "isolatedModules": true,
+    "moduleDetection": "force",
+    "noEmit": true,
+    "jsx": "react-jsx",
+
+    "strict": true,
+    "noUnusedLocals": true,
+    "noUnusedParameters": true,
+    "noFallthroughCasesInSwitch": true,
+    "verbatimModuleSyntax": true,
+
+    "baseUrl": ".",
+    "paths": {
+      "@/*": ["src/*"]
+    }
+  },
+  "include": ["src", "vite.config.ts"]
+}