fix(tui): stop completion mangling column names that need quoting (T1) - #57

Completion had two independent backward scanners from the cursor. The
parser decided *what* to suggest; extract_partial_word_at_cursor in
text_operations.rs independently decided *what span to replace*. They
disagreed whenever quotes or dots were involved.

On data/countries.csv (name.common, idd.root, translations.ara.official):

  SELECT name.<tab>     offered Contains('') instead of the columns
  SELECT name.com<tab>  offered nothing at all
  SELECT "na<tab>       produced SELECT name.common"  (quote eaten)
  SELECT na<tab><tab>   produced SELECT "name.commonname.official"

So every column that has to be quoted was effectively unreachable by
completion, and cycling corrupted the buffer.

Introduce src/sql/completion_token.rs: one quote- and dot-aware scanner
both halves share, handling an open quote, a cursor just past a closing
quote, and a bare identifier where dots are part of the name. Add
ParseResult::replace_start so the parser hands the editor the byte span
to splice over instead of the editor guessing, threaded through
HybridResult and CompletionState so it survives Tab cycling.

complete_dotted_column resolves dotted text that prefixes a real column;
text matching no column (capital.Con, 1.5, t.name) falls through to the
existing method-call handling unchanged.

Also replaces ~55 lines of tangled quote-matching in the suggestion
filter with a single unquoted comparison, and deletes the now-unused
extract_partial_word_at_cursor - leaving a superseded duplicate scanner
in place is how this regresses.

Adds docs/TUI_FEATURES.md, a T-numbered book of work for the interactive
editor alongside the P (parity) and R (refactoring) logs. The TUI has no
equivalent of the parity harness, so its defects only surface in use;
T2-T6 record what this fix uncovered, including that get_property_type
is still a hardcoded list of trade-desk column names.

Tests: tests/dotted_column_completion.rs (12) covers both halves - what
is suggested and what the buffer ends up containing - plus 9 unit tests
for the scanner. Full suite green, no new clippy warnings.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0152wRProARq2WGPss4698iY