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).

CHANGELOG.md

@@ -21,6 +21,14 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   foreground/background contrast and its syntax-colour distinctness verified
   on each build.
 
+### Removed
+- The `blob` column type. It could be declared but never given a value
+  (there was no way to type a binary value in either mode), so it was a
+  dead end with nothing to teach. The vocabulary is now nine types.
+  Existing projects that used a `blob` column still open — the column is
+  converted to `text` on first load (a backup of the original project file
+  is kept alongside it).
+
 ### Fixed
 - Pasting or scripting several commands at once no longer occasionally
   rejects a valid simple-mode `insert` — submitted right after adding a