📝 Rename test-loop "blue" phase to "type"; cite TDD

The type-first spec step was labelled "Blue", which collides with the
Red-Green-Blue convention where blue means the refactor phase (and our
loop already has an explicit Refactor step). Rename phase 1 to Type and
describe the loop as type -> red -> green -> refactor.

Tie the discipline to its established name: Type-Driven Development
(Edwin Brady), quoting the Idris framing -- treat the type as the plan,
let the compiler/type-checker drive you to a program that satisfies it.
Section heading becomes "Testing discipline (type-driven)"; update the
AGENTS.md pointer + anchor. Add "idris" to the cspell dictionary.

De-duplicate: CONTRIBUTING.md no longer re-lists the banned directives
(@ts-ignore, as casts, ...); it links to AGENTS.md "Never do", the
single home for that rule, so the lists can't drift.

AGENTS.md

@@ -35,7 +35,7 @@ Never start a long-lived / blocking process such as `npm run watch`. It runs unt
 ## Read these
 
 - [CONTRIBUTING.md § Rules the tools don't enforce](./CONTRIBUTING.md#rules-the-tools-dont-enforce) — the constraints the linters don't catch; CI/review bounce these. **The most important section.**
-- [CONTRIBUTING.md § Testing discipline (type-first)](./CONTRIBUTING.md#testing-discipline-type-first) — write the `expectTypeOf` (blue) before the `assert` (red); the types are the feature.
+- [CONTRIBUTING.md § Testing discipline (type-driven)](./CONTRIBUTING.md#testing-discipline-type-driven) — write the `expectTypeOf` (type) before the `assert` (red); the types are the feature.
 - [CONTRIBUTING.md § Script prefix convention](./CONTRIBUTING.md#script-prefix-convention) — adding an `npm run` script? reuse an existing prefix or it doesn't belong.
 - [CONTRIBUTING.md § Commit messages](./CONTRIBUTING.md#commit-messages) — gitmoji + imperative + 50/72.
 - [CONTRIBUTING.md § Feedback tiers](./CONTRIBUTING.md#feedback-tiers) — what runs when and at what cost (`watch` / pre-commit / pre-push / `check` / `verify` / `fix` / `maintain` / CI).