ADR-0022 follow-up r3: identifier colour, NewName hint, "Next:" wording, "type" label

Three fixes from a third round of real testing.

1. **tok_identifier vivid (round-3 #1).** The cool grey-blue
   from r2 was still too close to theme.fg to register as
   distinct. Bumped to cyan-teal (#56B6C2 dark / #0F6B76
   light) — identifiers are the user's most "special" content
   and now read that way against keywords (purple), numbers
   (orange), strings (green), and flags (amber).

2. **"Type a name" hint at NewName slots (round-3 #2).**
   New `completion::typing_name_at_cursor(input, cursor)`
   returns `Some(TypingName)` when the cursor sits at — or
   inside — an `IdentSlot::NewName` position. It probes by
   substituting a single-letter placeholder identifier and
   re-parsing to discover what the parser would expect AFTER
   the name; the hint then reads "Type a name, then `(`"
   instead of the technical "next: `(`" that surfaces once
   the partial identifier has been consumed by the live
   parser. When the probe yields nothing useful (custom
   errors with empty expected, or a complete-on-substitute
   case), falls back to "Type a name".

   New catalog keys hint.ambient_typing_name and
   hint.ambient_typing_name_then. Wired into ambient_hint
   between the candidate-list and invalid-ident checks.

3. **"Next:" instead of "expected:" wording.** "Expected"
   read as a leaked diagnostic; "Next:" is shorter,
   conversational, and consistent with the action-oriented
   voice of "Submit with Enter" and "Type a name". Hint
   sentences now also start capitalised
   (Submit/Next/Type/No-such), per the user's Capital-T-on-
   "type a name" preference.

4. **type_keyword labelled "type".** Without a label, the
   `select_ref!` over an Identifier token produced
   `RichPattern::SomethingElse`, which rendered as the
   meaningless "something else" in the hint after `(`.
   Labelled now: error reads "Next: type" — terse but
   honest. The label is applied BEFORE try_map (not after,
   not via as_context) so the existing custom-error wording
   for unknown types ("unknown type 'varchar' (expected one
   of: …)") still surfaces unchanged.

Tests: 755 passing, 0 failing, 1 ignored (no net change —
+5 typing_name cases, -0 net since one test was reworded
for capitalisation rather than added). Clippy clean.

Smoke probe verifies: "add column to table T: " → "Type a
name, then `(`"; "add column to table T: Name (" → "Next:
type"; "show data Custp" → "No such table: `Custp`"; valid
input → "Submit with Enter".

Note for next testing round: parser-side custom errors
(e.g. the "tables need at least one column" message that
fires for `create table Customers `) still read in
lowercase — they're hand-written in parser.rs source rather
than via the catalog. If the lowercase "tables need…"
intrusion bothers you, easy follow-up.

src/theme.rs

@@ -70,7 +70,7 @@ impl Theme {
             // accent tones; keyword takes a cool accent tone
             // distinct from the mode-banner blue.
             tok_keyword: Color::Rgb(0xC7, 0x92, 0xEA),    // muted purple
-            tok_identifier: Color::Rgb(0xAB, 0xB2, 0xBF), // cool grey-blue (distinct from fg)
+            tok_identifier: Color::Rgb(0x56, 0xB6, 0xC2), // cyan-teal — identifiers are the user's content, deserve a vivid distinct colour
             tok_number: Color::Rgb(0xF7, 0x8C, 0x6C),     // warm orange
             tok_string: Color::Rgb(0xC3, 0xE8, 0x8D),     // soft green
             tok_punct: Color::Rgb(0x8B, 0x90, 0x9A),      // == muted
@@ -96,7 +96,7 @@ impl Theme {
             // identifier/punct close to fg/muted; warm tones for
             // literals + flags; cool accent for keyword.
             tok_keyword: Color::Rgb(0x6F, 0x42, 0xC1),    // royal purple
-            tok_identifier: Color::Rgb(0x3F, 0x47, 0x57), // dark steel-blue (distinct from fg)
+            tok_identifier: Color::Rgb(0x0F, 0x6B, 0x76), // deep teal — same role as dark variant: identifiers stand out
             tok_number: Color::Rgb(0xBC, 0x4F, 0x1F),     // burnt orange
             tok_string: Color::Rgb(0x22, 0x86, 0x3A),     // forest green
             tok_punct: Color::Rgb(0x60, 0x66, 0x73),      // == muted