fix(classifier): feature verb wins over debug keyword (part of #196)

[iamtoruk]

First of three PRs addressing the issues flagged in #196 and #159. Independent of the others; can land alone.

The bug

Messages like `add error handling`, `create an issue tracker`, or `implement the 404 page` were landing in the Debugging bucket because the classifier checked the debug regex before the feature regex. Real users from #196 saw their feature work mislabeled.

```ts
// Before: order of checks decided the result
if (DEBUG_KEYWORDS.test(userMessage)) return 'debugging' // wins on "add error handling"
if (REFACTOR_KEYWORDS.test(userMessage)) return 'refactoring'
if (FEATURE_KEYWORDS.test(userMessage)) return 'feature'
```

The fix

Pick whichever keyword pattern matches earliest in the user message. The position of the leading verb is a much stronger intent signal than the order of the checks in code.

```ts
// After: position decides
return firstMatchingCategory(userMessage, [
{ regex: REFACTOR_KEYWORDS, category: 'refactoring' },
{ regex: FEATURE_KEYWORDS, category: 'feature' },
{ regex: DEBUG_KEYWORDS, category: 'debugging' },
]) ?? 'coding'
```

Tie-break (same start index) goes to the candidate listed first. Ordering is `refactoring > feature > debugging` so existing behavior for plain bug reports (`login is broken, traceback below`) is preserved — DEBUG word leads in those cases.

Same logic applied to `classifyConversation` for chat-only turns.

Examples

Message	Before	After
`add error handling`	debugging	feature
`create an issue tracker`	debugging	feature
`implement the 404 page`	debugging	feature
`fix the layout for the new feature`	debugging	debugging (unchanged)
`login is broken, traceback below`	debugging	debugging (unchanged)
`refactor the error handling`	refactoring	refactoring (unchanged)

Tests

8 new regression tests under `describe('classifyTurn — feature vs debugging precedence (#196)')`. Full suite: 45 files / 609 tests, all pass.

Out of scope

• Cursor per-project breakdown (separate PR — addresses the other half of Counting does not work at all #196 and feeds into Issue: Cursor Cost Tracking Not working #159).
• Cursor model alias completeness (separate PR — addresses Issue: Cursor Cost Tracking Not working #159).