chore: remove dead files and unused barrel index re-exports

[aaight]

Summary

Removes 3 dead files and 5 unused barrel/index re-exports to lean up the codebase and make it easier to navigate.

Dead files deleted:

• src/db/schema/credentials.ts — stub file with only comments, no exports, never imported
• src/agents/shared/taskPrompts.ts — both exports (buildCheckFailurePrompt, buildDebugPrompt) have zero production callers
• tests/unit/agents/shared/taskPrompts.test.ts — companion test for the dead module above

Unused barrel/index files deleted:

• src/trello/index.ts — all consumers import from trello/client.js directly
• src/db/index.ts — all consumers import from sub-modules directly
• src/gadgets/index.ts — all consumers import individual gadget files
• src/agents/index.ts — consumers import from agents/registry.js and agents/prompts/index.js
• src/config/index.ts — consumers import from specific config files

Note: src/gadgets/shared/index.ts was listed in the card but was found to be actively imported by 6 gadget files (WriteFile.ts, FileInsertContent.ts, FileRemoveContent.ts, FileMultiEdit.ts, AstGrep.ts, FileSearchAndReplace.ts) so it was NOT deleted.

Test plan

• npm run typecheck — passes with zero errors
• npm run lint — passes with zero errors
• npm test — all 289 test files / 5408 tests pass
• Grep confirms no remaining imports reference deleted files

Trello card: https://trello.com/c/69b835ff979fc15f0cfc4b8e

🕵️ claude-code · claude-sonnet-4-6 · run details

[nhopeatall]

LGTM — clean dead code removal. Verified all claims:

• All 8 deleted files have zero remaining imports (static or dynamic) across the codebase
• buildCheckFailurePrompt and buildDebugPrompt have zero production callers
• src/db/schema/credentials.ts was a comment-only stub never exported by the schema barrel
• All 5 barrel index files were unused — consumers already import from specific sub-modules directly
• The deleted test file's coverage of renderInlineTaskPrompt/renderCustomPrompt is redundant with prompts.test.ts and profiles.test.ts
• All CI checks pass (typecheck, lint, 5408 tests)
• src/gadgets/shared/index.ts correctly retained (confirmed 6 active importers)

🕵️ claude-code · claude-opus-4-6 · run details