Regression: apostrophes in prompt prose disable subsequent @file completion

[breedx]

Summary

After 029ca24, an apostrophe in ordinary prompt prose can prevent a later @file token from offering completions.

For example, with target.py available in the current directory/index:

• read @target offers target.py.
• don't change @target offers no candidates.
• it's in @target also offers no candidates.

The cursor is at the end of each prompt.

Expected behavior

A contraction in preceding prose should not prevent completion of a later attachment token. Quoted and escaped filenames should continue to work, and email addresses or prose following a completed attachment should not be treated as active references.

Reproduction and verification

Reproduced using the real FilePathCompleter.get_completions with an injected file-index snapshot containing target.py, with background indexing disabled to make the test deterministic:

1. Set the current directory and the snapshot root to the same temporary directory.
2. Set the indexed paths to ["target.py"].
3. Request completions for Document("don't change @target") with the cursor at the end.
4. Observe an empty list instead of a completion for target.py.

The same completer probe returns target.py at pre-change commit 370c8b4fb195ff1215f63d706b190455d2147ff2; it returns no candidates at 1d25d696 containing the change.

The parser itself also demonstrates the failure:

• active_reference("read @target") returns ("target", 6).
• active_reference("don't change @target") returns None.

This was verified through parser/completer calls on Linux, not a full interactive TUI test.

Likely cause

code_puppy/file_completion_tokens.py:25-26 treats every apostrophe or double quote in the entire preceding prompt as a quote delimiter. The apostrophe in don't opens quote state; subsequent spaces no longer advance the active token boundary, so the later @target is not recognized.

Please scope filename quote/escape handling to the active attachment token, or otherwise distinguish contractions in surrounding prose from quoted paths. Add regression coverage for contractions before @file, alongside the existing quoted/escaped-path and token-boundary tests.