fix(tui): quote column names when expanding SELECT * (T8)

[TimelordUK]

Ctrl+X (expand to all schema columns) and Alt+X (expand to visible columns) both did columns.join(", ") on the raw names. On data/countries.csv that produced

SELECT name.common, name.official, tld, ..., idd.root, ... FROM countries

which the parser reads as method calls on a name column. Every dotted name - name., idd. and 60-odd translations.., i.e. most of the file - came out unusable, and the next keystroke was to hand-quote 70 columns or undo.

This is T1 in a different hat. Completion had already been taught to quote (quote_if_needed at nine sites in cursor_aware_parser.rs); expansion is the other producer of column text and never learned. Two producers, one of them right, is exactly the drift T1's "the parser owns semantics, the editor owns text" principle is meant to stop - it just had nowhere to put the rule.

Introduce src/sql/identifier.rs, the single home for does this name have to be quoted. The rule mirrors Lexer::read_identifier, which is what actually decides whether a bare word survives: Unicode alphanumerics plus underscore, not starting with a digit. Keyword status comes from Token::from_keyword rather than a second hand-kept list, so a column called row or end is quoted for exactly as long as the lexer reserves those words.

Three call sites now share it:

csv_fixes::needs_quoting (used by all of completion) was a 9-way
contains() chain that missed leading digits and keywords - delegates.

formatter::needs_quotes had its own 40-word reserved list, hand-kept -
delegates, and stops re-quoting text the parser already handed back
quoted.

Buffer::expand_asterisk{,_visible} did nothing at all - quotes.

Left open, deliberately: formatter::needs_quotes is applied to SelectStatement::columns, the deprecated legacy field that can hold expression text, so the formatter still wraps COUNT(*) in quotes. That is a pre-existing bug about what it quotes rather than when, and it wants fixing where that field is retired.

Tests: tests/asterisk_expansion.rs (5) covers both expansion paths, hidden columns, the rest of the query surviving intact, and names that collide with keywords; src/sql/identifier.rs has 8 unit tests for the rule itself. Verified end to end by running the full 76-column expansion of data/countries.csv. Full suite green, fmt clean, no new clippy warnings.

Claude-Session: https://claude.ai/code/session_01WjekXbE7Y1Gu4H7Pr6T8is