fix: drop better-sqlite3 to remove deprecated prebuild-install (#75)

npm was warning on every install that prebuild-install@7.1.3 is no
longer maintained. prebuild-install ships as a transitive dependency
of better-sqlite3 and upstream PR #1446 to replace it is still open,
so we switch to Node's built-in node:sqlite module (stable in Node 24,
experimental in Node 22/23) and remove the better-sqlite3 dep entirely.

- src/sqlite.ts: uses DatabaseSync from node:sqlite. The one-shot
  ExperimentalWarning about SQLite on Node 22/23 is silenced for that
  specific warning; other warnings pass through unchanged.
- package.json: engines.node bumped to >=22 (Node 20 EOL 2026-04-30),
  better-sqlite3 and @types/better-sqlite3 removed, @types/node added
  (it was coming in transitively via @types/better-sqlite3).
- tests/providers/opencode.test.ts: fixture DB creation switched to
  node:sqlite (API parity for the CREATE TABLE + INSERT + prepare
  path we use).

End-user install footprint shrinks from 167 to 40 packages and prints
zero deprecation warnings.

Credit: @primeminister for the report.

package.json

@@ -1,6 +1,6 @@
 {
   "name": "codeburn",
-  "version": "0.7.2",
+  "version": "0.7.3",
   "description": "See where your AI coding tokens go - by task, tool, model, and project",
   "type": "module",
   "main": "./dist/cli.js",
@@ -29,7 +29,7 @@
     "developer-tools"
   ],
   "engines": {
-    "node": ">=20"
+    "node": ">=22"
   },
   "author": "AgentSeal <hello@agentseal.org>",
   "license": "MIT",
@@ -39,11 +39,8 @@
     "ink": "^7.0.0",
     "react": "^19.2.5"
   },
-  "optionalDependencies": {
-    "better-sqlite3": "^12.0.0"
-  },
   "devDependencies": {
-    "@types/better-sqlite3": "^7.6.0",
+    "@types/node": "^22.19.17",
     "@types/react": "^19.2.14",
     "tsup": "^8.4.0",
     "tsx": "^4.19.0",