fix(core): use bcode database filename

[Alezander9]

Summary:

• Restore BrowserCode database filenames in the new core database path owner.
• Add a focused Database.path test for bcode.db and bcode-.db behavior.

Context:

• The upstream v1.17 sync moved DB path ownership from packages/opencode/src/storage/db.ts to packages/core/src/database/database.ts and accidentally reintroduced opencode.db.
• BrowserCode memory documents bcode.db as the intended branding invariant.

Tests:

• bun test test/database-path.test.ts (packages/core)
• bun typecheck (packages/core)
• pre-push filtered bun turbo typecheck

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Summary by cubic

Restore BrowserCode database filenames in packages/core: use bcode.db and bcode-<channel>.db instead of opencode.db, fixing a regression from the v1.17 sync.

• Bug Fixes
  • Updated Database.path() to return bcode.db or bcode-<channel>.db, and honor OPENCODE_DISABLE_CHANNEL_DB.
  • Added packages/core/test/database-path.test.ts to cover default and env-var behavior.

^{Written for commit 5da41a9. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 2 files

_{Re-trigger cubic}