feat(types)!: drop the blob column type (ADR-0005 Amendment 2)

blob was a dead-end: declarable but never fillable (no literal in either
mode, seed-unsupported), so a blob column could only ever hold NULL. Remove
Type::Blob + Value/CellValue::Blob + the base64 CSV path + the grammar slot
+ completion/render/type-change/seed handling + the binder refusal (whose
message also carried a user-facing "DSL" copy-rule bug). The vocabulary is
now nine types; base64 stays (clipboard OSC-52).

Backward compat is the ADR-0015 migration framework's first real use: a
v1->v2 format bump (CURRENT_SCHEMA_VERSION across serializer/parser/skeleton)
with a migrator that rewrites `type: blob` -> `type: text`, and a forced .db
rebuild from the migrated text when a blob column was actually converted
(the stale .db keeps a STRICT BLOB engine column). Conversion to text is
non-destructive and CSV-free. Covered by a full-stack integration test and a
Tier-4 PTY test that opens a real legacy v1-blob project.

Also sweeps the nine-type vocabulary through CLAUDE.md, requirements.md, the
website (type reference, seed doc, highlight grammar), and the ADR-0030/0033/
0035 cross-references; CHANGELOG Removed entry; handoff-79.

BREAKING CHANGE: the `blob` column type is removed. Existing projects that
declared a blob column are migrated on first open (the column becomes text;
the original project.yaml is kept as a .v1.bak).

src/dsl/walker/mod.rs

@@ -240,7 +240,6 @@ const fn catalog_key_for_value_type(ty: crate::dsl::types::Type) -> &'static str
         Type::Text => "hint.value_slot_text",
         Type::Date => "hint.value_slot_date",
         Type::DateTime => "hint.value_slot_datetime",
-        Type::Blob => "hint.value_slot_blob",
         Type::Serial => "hint.value_slot_serial",
         Type::ShortId => "hint.value_slot_shortid",
     }
@@ -4745,7 +4744,6 @@ mod tests {
             (Type::Text, "hint.value_slot_text"),
             (Type::Date, "hint.value_slot_date"),
             (Type::DateTime, "hint.value_slot_datetime"),
-            (Type::Blob, "hint.value_slot_blob"),
         ] {
             let schema = schema_with("T", &[("c", ty)]);
             let mode = hint_mode_at_input_with_schema("insert into T values (", &schema);