ADR-0024 Phase F (full) step 3: delete legacy parser modules

Removes the last consumers of `dsl::lexer`, `dsl::keyword`, and
`dsl::ident_slot`, then deletes the modules.

- `Theme::token_color(&TokenKind)` deleted along with its test;
  `Theme::highlight_class_color(HighlightClass)` is the sole
  highlight-colour mapper (the walker's `per_byte_class` feeds
  it directly).
- `IdentSource` (`dsl::grammar`) absorbs the schema-list /
  expected-label / round-trip semantics that previously lived
  on `IdentSlot`. Adds `completes_from_schema`, `expected_label`,
  and `from_expected_label` methods. The walker's
  `Expectation::Ident { source }` and the schema-lookup request
  on the database worker now share one enum.
- `SchemaCache::for_slot(IdentSlot)` → `for_source(IdentSource)`.
- `Database::list_names_for` and the `Request::ListNamesFor`
  worker variant take `IdentSource`. Internal tables and column
  / relationship lookups dispatch on the same enum.
- `InvalidIdent.slot: IdentSlot` → `InvalidIdent.source: IdentSource`.
  The `invalid_ident_at_cursor` rendering branch in
  `input_render.rs::ambient_hint` updates accordingly.
- Completion's keyword filter (`Keyword::from_word`) becomes
  "backticked items whose payload is all ASCII alphabetic" —
  punct and digit literals still surface through their own
  candidate sources (composite-literal, flag, schema-ident);
  the alphabetic filter excludes them from the keyword bucket.
- `friendly::keys::tests::keyword_and_punct_have_complete_token_vocabulary`
  is dropped. It cross-checked `Keyword::ALL` / `Punct::ALL`
  against catalog entries; both enums are gone. The
  `parse.token.keyword.*` / `parse.token.punct.*` catalog
  entries themselves survive for one more commit (catalog
  cleanup, ADR-0024 §cleanup-pass); the
  `keys_validate_against_catalog` test still pins them.
- Modules deleted: `src/dsl/lexer.rs`, `src/dsl/keyword.rs`,
  `src/dsl/ident_slot.rs`.

Tests: 806 passing, 0 failing, 1 ignored. The drop from 852
reflects the removed module-internal tests (~32 lexer, 7
keyword, 4 ident_slot, 1 theme token_color, 1 friendly keys
keyword/punct), and is the expected outcome.

Clippy clean with `nursery` lints + `-D warnings`.

src/friendly/keys.rs

@@ -459,42 +459,19 @@ pub const KEYS_AND_PLACEHOLDERS: &[(&str, &[&str])] = &[
 #[cfg(test)]
 mod tests {
     use super::KEYS_AND_PLACEHOLDERS;
-    use crate::dsl::keyword::{Keyword, Punct};
     use crate::friendly::format::catalog;
     use std::collections::HashSet;
 
-    /// Every `Keyword` variant must have a
-    /// `parse.token.keyword.<name>` entry; every `Punct`
-    /// variant must have a `parse.token.punct.<name>` entry.
-    /// Catches the case where a keyword or punct is added to
-    /// the macro but not to the catalog (ADR-0021 §7).
-    #[test]
-    fn keyword_and_punct_have_complete_token_vocabulary() {
-        let declared: HashSet<&str> =
-            KEYS_AND_PLACEHOLDERS.iter().map(|(k, _)| *k).collect();
-        let mut missing: Vec<String> = Vec::new();
-        for &(kw, _) in Keyword::ALL {
-            let key = kw.catalog_token_key();
-            if !declared.contains(key.as_str()) {
-                missing.push(format!(
-                    "Keyword::{kw:?} ⇒ catalog key `{key}` not declared in keys.rs"
-                ));
-            }
-        }
-        for &(p, _, _) in Punct::ALL {
-            let key = p.catalog_token_key();
-            if !declared.contains(key.as_str()) {
-                missing.push(format!(
-                    "Punct::{p:?} ⇒ catalog key `{key}` not declared in keys.rs"
-                ));
-            }
-        }
-        assert!(
-            missing.is_empty(),
-            "token vocabulary incomplete:\n  {}",
-            missing.join("\n  "),
-        );
-    }
+    // The pre-Phase-F `keyword_and_punct_have_complete_token_vocabulary`
+    // test cross-checked the `Keyword` / `Punct` enums against
+    // `parse.token.keyword.*` / `parse.token.punct.*` catalog
+    // keys. With those enums deleted (ADR-0024 §migration Phase F)
+    // and the walker rendering keyword wording via
+    // `format!("`{word}`")`, the catalog entries survive only as
+    // historic vocabulary; the `keys_validate_against_catalog`
+    // test below still asserts every key in `KEYS_AND_PLACEHOLDERS`
+    // resolves and vice versa, which keeps the catalog itself
+    // honest. The dead entries collapse in ADR-0024 §cleanup-pass.
 
     /// Walks `KEYS_AND_PLACEHOLDERS` and verifies every entry
     /// matches the catalog. ADR-0019 §8.6.