refactor: enforce ktx naming and AGENTS.md compliance sweep (#289)

Align the tree with AGENTS.md/CLAUDE.md conventions:

- Rewrite user-facing strings, docs, and tests to lowercase `ktx`
  (no bare uppercase `KTX` tokens remain outside literal identifiers).
- Drop the legacy `historicSql` migration path and its now-unused
  helpers, per the no-backward-compat rule.
- Remove `as unknown as` / `any` casts: narrow `BaseTool` generics to
  `z.ZodObject`, add a typed `createLookerClient`, and delete the dead
  `getParametersSchema`/`toAnthropicFormat` pre-AI-SDK helpers.
- Use `InvalidArgumentError` for Commander parse failures.
- Finish the adapter→connector prose conversion in the `ktx.yaml` docs
  while keeping the literal `adapters` config key.

docs-site/content/docs/getting-started/quickstart.mdx

@@ -307,12 +307,12 @@ connection is unreachable or misconfigured the build is blocked up front and
 **ktx** names the failing connection by id and connector type:
 
 ```text
-KTX cannot build context: a required connection failed its live test.
+ktx cannot build context: a required connection failed its live test.
 
 Failed connections:
   warehouse (postgres)
 
-Each connection must be reachable before KTX builds context.
+Each connection must be reachable before ktx builds context.
 Run `ktx connection test <id>` to see the error, fix the connection, then retry.
 ```