ADR-0022 stage 8e: invalid-identifier detection + hint variant

Per the user's #5: "if our candidate selection works
correctly, then entering a character that removes all matches
is the same as entering an invalid token." Closes the loop
between schema cache (8c/8d) and live error feedback (4).

New `completion::invalid_ident_at_cursor(input, cursor, cache)`
returns `Some(InvalidIdent { range, found, slot })` when:
  - the cursor is on a partial identifier-shaped token;
  - the parser's expected-set at the start of that token
    contains a known-set IdentSlot (TableName / Column /
    RelationshipName);
  - no schema entry across those slots prefix-matches the
    typed text.

`render_input_runs` extended to take a `&SchemaCache` and
overlay the invalid-identifier range with `tok_error` —
same visual treatment as the parse-error overlay (4),
unified red signal regardless of which detector fires.

`ambient_hint` extended to surface `hint.ambient_invalid_ident`
when invalid_ident_at_cursor returns Some — wording
"no such {kind}: `{found}`" mirrors ADR-0019's engine-error
voice for consistency. Catalog + KEYS_AND_PLACEHOLDERS
declaration added; validator passes.

Render priority: candidates win over invalid-ident
(if any schema match exists for the partial prefix, the
state is "in-progress completion" not "invalid"). Falls
through to the existing parse-error/incomplete/Valid
framings otherwise.

NewName slots are filtered out at the source — typing
into a "user invents this name" position is never invalid
(per `IdentSlot::completes_from_schema`).

Tests: 744 passing, 0 failing, 1 ignored (738 baseline →
+6: 5 invalid_ident_at_cursor cases covering
unknown-prefix-fires, prefix-match-doesn't-fire,
NewName-immune, no-cursor-token, keyword-slot-immune;
plus 1 ambient_hint integration test). Clippy clean.

This closes ADR-0022. Stages 1-8e together deliver the
ambient-typing-assistance feature: token highlighting,
error overlay, hint panel ambient, hint panel multi-
candidate display with scroll markers, Tab/Shift-Tab
cycling with one-keystroke Esc/Backspace undo, schema-aware
identifier completion, and invalid-identifier live
feedback. Total stage-8 footprint: 5 commits, ~1600 lines.

src/friendly/strings/en-US.yaml

@@ -258,6 +258,10 @@ hint:
   ambient_complete: "submit with Enter"
   ambient_expected: "expected: {expected}"
   ambient_error_with_usage: "{message} — usage: {usage}"
+  # Invalid identifier in a schema slot (ADR-0022 stage 8e
+  # + the user's #5). Voice mirrors ADR-0019's "no such
+  # {kind}" wording for consistency with engine errors.
+  ambient_invalid_ident: "no such {kind}: `{found}`"
 
 parse:
   # Wrapper around chumsky's structural error message. The