ADR-0024 Phase D: per-column-type hint prose at value slots

The Phase D commit landed parse-time validation but not the
user-facing payoff — per-column-type hints. Typing
`insert into Customers values (` rightfully expected a hint
like "Type an integer (e.g. 42, -7) or null" at an int column.
This commit closes that gap.

End-to-end:

**`Node::TypedValueSlot { ty, inner }`** (new variant in
`src/dsl/grammar/mod.rs`):
- Walker walks `inner` to consume the literal but tags
  `WalkContext::pending_value_type = Some(ty)` on entry, then
  clears it on a successful inner match. Positions BETWEEN
  slots (`insert into T values (1` mid-input) thus don't carry
  a stale hint type.

**Typed slot factories wrapped in `TypedValueSlot`**
(`src/dsl/grammar/shared.rs`):
- `INT_SLOT`, `REAL_SLOT`, `DECIMAL_SLOT`, `BOOL_SLOT`,
  `TEXT_SLOT`, `DATE_SLOT`, `DATETIME_SLOT`, `BLOB_SLOT`,
  `SERIAL_SLOT`, `SHORTID_SLOT` — each pairs an inner literal
  Choice with its `Type` so the walker can tag context.
- `slot_for_type(ty)` dispatches to the appropriate constant.
- Bug fix: `ShortId` previously dispatched to `INT_SLOT` (a
  pre-Phase-D holdover from the chumsky-side generic
  fallback). `shortid` columns store base58 text (ADR-0011
  fk_target_type shortid → text); the corrected slot accepts
  `StringLit` or `null`.

**Schema-aware hint resolver** (`src/dsl/walker/mod.rs`):
- `hint_mode_at_input_with_schema(source, &SchemaCache) ->
  Option<HintMode>` is the new public entry point. Reads
  `pending_value_type` from the walker's WalkContext and
  emits `HintMode::ProseOnly("hint.value_slot_<type>")` —
  one per Type.
- The schemaless `hint_mode_at_input(source)` falls back to
  the generic `hint.value_literal_slot` at value-literal slots
  (no per-type narrowing without a schema).
- `catalog_key_for_value_type(ty)` is the type → key
  dispatcher.

**Catalog entries** (`src/friendly/strings/en-US.yaml`,
`src/friendly/keys.rs`):
- 10 new `hint.value_slot_<type>` keys with per-type prose:
  - int/serial → "Type an integer (e.g. 42, -7) or null"
  - real/decimal → "Type a number (e.g. 3.14, -0.5) or null"
  - bool → "Type true, false, or null"
  - text → "Type a quoted string (e.g. 'Alice') or null"
  - date → "Type a quoted date as 'YYYY-MM-DD' or null"
  - datetime → "Type a quoted datetime as 'YYYY-MM-DD
    HH:MM:SS' or null"
  - blob → "Type a quoted blob literal or null"
  - shortid → "Type a quoted shortid (or omit to auto-generate)
    or null"

**Ambient-hint dispatch** (`src/input_render.rs::ambient_hint`):
- Passes the SchemaCache through to
  `hint_mode_at_input_with_schema`, so the live hint panel
  surfaces per-column-type prose as the user types into a
  value slot.

Tests:
- 8 walker-side tests cover insert / update / where typed-slot
  hint dispatch, mid-value no-stale-hint behaviour, and a
  full-coverage routing matrix for every `Type` variant.
- 4 input_render integration tests cover the end-to-end
  ambient_hint path: insert first/second value, update set
  value, and the schemaless fallback to generic prose.

Tests: 842 passing, 0 failing, 1 ignored. Clippy clean.

For the user: typing `insert into Customers values (` against
a Customers table whose first column is `id:int` now shows
"Type an integer (e.g. 42, -7) or null" in the hint panel,
replacing the previous generic value-literal prose. After
typing `1, `, the panel updates to whatever the second column
requires — "Type a quoted string (e.g. 'Alice') or null"
for text, "Type a quoted date as 'YYYY-MM-DD'" for date, etc.

src/dsl/walker/driver.rs

@@ -130,6 +130,20 @@ pub fn walk_node(
             let resolved: &'static Node = Box::leak(Box::new(factory(ctx)));
             walk_node(source, pos, resolved, ctx, path, per_byte)
         }
+        Node::TypedValueSlot { ty, inner } => {
+            // ADR-0024 §Phase D §typed-value-slots. Tag the
+            // pending column type so the hint resolver can emit
+            // per-type prose at empty prefix. Clear on
+            // successful inner match — positions BETWEEN typed
+            // slots (post-comma, between values) don't carry a
+            // stale hint type.
+            ctx.pending_value_type = Some(*ty);
+            let result = walk_node(source, pos, inner, ctx, path, per_byte);
+            if matches!(result, NodeWalkResult::Matched { .. }) {
+                ctx.pending_value_type = None;
+            }
+            result
+        }
         Node::Flag(name) => walk_flag(source, pos, name, path, per_byte),
         Node::Repeated {
             inner,