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/dsl/grammar/mod.rs

@@ -49,32 +49,76 @@ pub enum HighlightClass {
 
 /// Where an `Ident` slot's candidates come from at completion time.
 ///
-/// Phase A only exercises `NewName` (the `import … as <target>`
-/// slot) and `Free` (the catch-all branch in `mode`/`messages`
-/// that funnels unknown values into a friendly validator). The
-/// schema-aware variants land in Phase B-D.
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+/// Drives both the walker's `Expectation::Ident { source }` (which
+/// the parse-error bridge maps to a human label) and the
+/// `SchemaCache` lookup the completion engine uses for Tab
+/// candidates. The `Free` and `NewName` variants do not query the
+/// schema — `NewName` is for slots where the user invents the
+/// identifier, `Free` is the catch-all branch in `mode`/`messages`
+/// that funnels unknown values into a friendly validator.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub enum IdentSource {
     /// User invents this name. No schema lookup; no completion
     /// candidates beyond the identifier shape itself.
     NewName,
-    /// Existing table name. Phase B+.
-    #[allow(dead_code)]
+    /// Existing table name.
     Tables,
-    /// Existing column in the current table. Phase B+.
-    #[allow(dead_code)]
+    /// Existing column in the current table.
     Columns,
-    /// Existing relationship name. Phase B+.
-    #[allow(dead_code)]
+    /// Existing relationship name.
     Relationships,
-    /// Closed set from `Type::all()`. Phase B+.
-    #[allow(dead_code)]
+    /// Closed set from `Type::all()` — surfaced by the walker's
+    /// content validator on column-type slots; not user-listable
+    /// from the schema.
     Types,
     /// Any identifier shape; used by synthetic catch-all branches
     /// (e.g., the unknown-value branch of `mode <value>`).
     Free,
 }
 
+impl IdentSource {
+    /// Whether this source can be completed from the schema
+    /// cache (i.e. the candidate list comes from existing
+    /// entities rather than user invention or a closed set).
+    #[must_use]
+    pub const fn completes_from_schema(self) -> bool {
+        matches!(self, Self::Tables | Self::Columns | Self::Relationships)
+    }
+
+    /// Human-facing label used in parse-error wording
+    /// ("expected table name") and in the completion engine's
+    /// round-trip from a textual `expected` entry back to a
+    /// source kind. `Free` and `Types` collapse to "identifier"
+    /// and "type" respectively.
+    #[must_use]
+    pub const fn expected_label(self) -> &'static str {
+        match self {
+            Self::NewName | Self::Free => "identifier",
+            Self::Tables => "table name",
+            Self::Columns => "column name",
+            Self::Relationships => "relationship name",
+            Self::Types => "type",
+        }
+    }
+
+    /// Inverse of `expected_label`. Used by the completion engine
+    /// to recover the source kind from the `ParseError::Invalid::
+    /// expected` strings the walker bridge produces. `"identifier"`
+    /// maps to `NewName` (the only writeable label that uses that
+    /// wording in production grammars today).
+    #[must_use]
+    pub fn from_expected_label(label: &str) -> Option<Self> {
+        match label {
+            "identifier" => Some(Self::NewName),
+            "table name" => Some(Self::Tables),
+            "column name" => Some(Self::Columns),
+            "relationship name" => Some(Self::Relationships),
+            "type" => Some(Self::Types),
+            _ => None,
+        }
+    }
+}
+
 /// Hint-panel mode for an expected node.
 ///
 /// Phase A defaults to `Default`; the `ProseOnly` variant