feat: give column data types a dedicated syntax-highlight colour

Both Node::Ident and Word carried a highlight_override field, and
both were dead — the walker driver discarded the Ident's and
walk_word hardcoded Keyword. So column types (int, serial, …)
rendered identically to table/column names.

Wire both overrides through, and add a dedicated HighlightClass::Type
with its own theme colour (tok_type), distinct from keyword-purple
and identifier-teal. The three type Ident slots opt in, so canonical
types and the advanced-mode single-word SQL aliases (float, varchar,
…) render as types; the two-word `double precision` alias opts in via
a new Word::type_keyword constructor. ADR-0022 Amendment 4.

docs/adr/README.md

@@ -27,7 +27,7 @@ This directory contains the project's ADRs, recorded per
 - [ADR-0019 — Friendly error layer (H1) and i18n message catalog](0019-friendly-error-layer-and-i18n.md)
 - [ADR-0020 — Tokenization layer for the DSL parser](0020-tokenization-layer-for-the-dsl-parser.md)
 - [ADR-0021 — Parser-as-source-of-truth for H1a (per-command usage in parse errors)](0021-parser-as-source-of-truth-for-h1a.md)
-- [ADR-0022 — Ambient typing assistance: colour, hint panel, completion (I3 + I4)](0022-ambient-typing-assistance.md) — **Amendment 1 supersedes §12's simple-mode-only carve-out**: the unified mode-aware walker (ADR-0030/0031/0032) now speaks SQL, so advanced-mode ambient assistance is re-enabled. `ambient_hint_in_mode` + `hint_resolution_at_input_in_mode` + `expected_for_hint_snapshot` thread `Mode`; `render_hint_panel` calls ambient for all modes (no more advanced-mode `None`); the one-shot `:` sigil is stripped before the ambient walk. Fixes a live bug where advanced-mode SQL hinting/completion-preview were dead despite Phase 2 marking them green (validated at the engine layer, not the UI). Simple-mode gating, highlighting, and the §13 performance posture are unchanged; covered by an app-level render test plus ambient-layer regression locks; **Amendment 2 reverses the handoff-14 keywords-first candidate ordering** — schema identifiers (table/column/relationship names) now sort *before* keywords so a name the user would have to look up stays visible in the single-row, window-scrolled candidate line (keywords are learned over time; the `tok_identifier`/`tok_keyword` colour split marks the boundary); shipped with a `walk_repeated` fix that surfaces a list item's trailing optionals at a clean boundary (`order by Name ` → `asc`/`desc`, `select Name ` → `as`, `create table … Code(text) ` → `not`/`unique`/`default`/`check`; the `,` separator deliberately not surfaced); records a deferred two-line hint box for growing lists; **Amendment 3 makes the ambient-hint fallback rung schema-aware** — Amendment 1's bottom-rung `parse_command_in_mode` was schemaless while every earlier rung was not, so between-values insert hints pointed at `)` (type-blind close) instead of `,` and wrong-arity closed tuples read "submit with Enter" for an input the schema-aware parse rejects (issue #2); now uses `parse_command_with_schema_in_mode`, no extra walk, with the friendly arity diagnostic still winning at its higher rung
+- [ADR-0022 — Ambient typing assistance: colour, hint panel, completion (I3 + I4)](0022-ambient-typing-assistance.md) — **Amendment 1 supersedes §12's simple-mode-only carve-out**: the unified mode-aware walker (ADR-0030/0031/0032) now speaks SQL, so advanced-mode ambient assistance is re-enabled. `ambient_hint_in_mode` + `hint_resolution_at_input_in_mode` + `expected_for_hint_snapshot` thread `Mode`; `render_hint_panel` calls ambient for all modes (no more advanced-mode `None`); the one-shot `:` sigil is stripped before the ambient walk. Fixes a live bug where advanced-mode SQL hinting/completion-preview were dead despite Phase 2 marking them green (validated at the engine layer, not the UI). Simple-mode gating, highlighting, and the §13 performance posture are unchanged; covered by an app-level render test plus ambient-layer regression locks; **Amendment 2 reverses the handoff-14 keywords-first candidate ordering** — schema identifiers (table/column/relationship names) now sort *before* keywords so a name the user would have to look up stays visible in the single-row, window-scrolled candidate line (keywords are learned over time; the `tok_identifier`/`tok_keyword` colour split marks the boundary); shipped with a `walk_repeated` fix that surfaces a list item's trailing optionals at a clean boundary (`order by Name ` → `asc`/`desc`, `select Name ` → `as`, `create table … Code(text) ` → `not`/`unique`/`default`/`check`; the `,` separator deliberately not surfaced); records a deferred two-line hint box for growing lists; **Amendment 3 makes the ambient-hint fallback rung schema-aware** — Amendment 1's bottom-rung `parse_command_in_mode` was schemaless while every earlier rung was not, so between-values insert hints pointed at `)` (type-blind close) instead of `,` and wrong-arity closed tuples read "submit with Enter" for an input the schema-aware parse rejects (issue #2); now uses `parse_command_with_schema_in_mode`, no extra walk, with the friendly arity diagnostic still winning at its higher rung; **Amendment 4 gives column types a dedicated highlight class** — both `Node::Ident.highlight_override` *and* the `Word.highlight_override` field were dead (driver destructured the former to `_`, `walk_word` hardcoded `Keyword`); now both wired through, with a new `HighlightClass::Type` + eighth `Theme` field `tok_type` (a pink/deep-magenta distinct from both keyword purple and identifier teal) so types no longer render identically to identifiers (issue #8); the three `IdentSource::Types` slots opt in via `Some(Type)` (advanced-mode single-word SQL aliases — `float`, `varchar`, … per ADR-0035 §3 — ride along for free), and the two-word `double precision` alias opts in via the new `Word::type_keyword` constructor so it matches its synonyms
 - [ADR-0023 — Unified declarative grammar tree](0023-unified-grammar-tree.md) — direction (superseded for execution detail by ADR-0024)
 - [ADR-0024 — Unified grammar tree: execution plan](0024-unified-grammar-tree-execution-plan.md) — **Accepted**, the executable spec — implemented (Phases A–F; Phase F shipped "minimal", `parser.rs` retained as the router — see the ADR's Phase F implementation note)
 - [ADR-0025 — Indexes](0025-indexes.md) — **Accepted** (**Amendment 1, 2026-05-25**: UNIQUE indexes admitted on the **advanced-mode** surface via `CREATE UNIQUE INDEX` — ADR-0035 §4d; the `IndexSchema.unique` flag round-trips through `project.yaml` with no new metadata table since the engine reports uniqueness natively; simple-mode `add unique index` stays deferred), `add index` / `drop index`, persistence, rebuild-table preservation, and items-list display (`C3` index portion + `S2`)