feat(lsp): add context-aware completion ranking and document highlights

Adds context-aware completion ranking and document highlights for Tcl.
Adds completion_context to distinguish variables and commands.
Wires per-file completion snapshots and ranking into the flow.
Adds document_highlight provider support and tests for highlights.

- Context-aware ranking of completion items using per-file snapshots
- Document highlight provider wired into initialization and tests
- Tests for completion context, ranking, and document highlights

server/src/tools/navigation.py

@@ -522,6 +522,37 @@ def matching_occurrences(
     return matches
 
 
+def document_highlights(
+    index: FileSymbolIndex,
+    identity: SymbolIdentity,
+    definitions: set[SymbolIdentity],
+) -> list[lsp.DocumentHighlight]:
+    """Return all occurrences of one symbol in the active document."""
+    highlights = []
+    for occurrence in index.occurrences:
+        if resolve_identity(occurrence, definitions) != identity:
+            continue
+
+        kind = lsp.DocumentHighlightKind.Text
+        if identity.kind == "variable":
+            kind = (
+                lsp.DocumentHighlightKind.Write
+                if occurrence.is_definition
+                else lsp.DocumentHighlightKind.Read
+            )
+        highlights.append(lsp.DocumentHighlight(range=occurrence.range, kind=kind))
+
+    return sorted(
+        highlights,
+        key=lambda highlight: (
+            highlight.range.start.line,
+            highlight.range.start.character,
+            highlight.range.end.line,
+            highlight.range.end.character,
+        ),
+    )
+
+
 def workspace_symbols(
     indexes: dict[str, FileSymbolIndex], query: str
 ) -> list[lsp.SymbolInformation]: