feat(setup): apply per-role LLM model presets, remove --llm-model (#268)

* feat(setup): write per-role llm model presets

* feat(setup): remove llm model setup flag

* chore(setup): update llm preset guidance

* docs(setup): document llm model presets

* chore(release): sync uv.lock to 0.9.0

* fix(cli): make sl query --execute work on secret-backed connections

sl query --execute used a parallel SQL executor (createDefaultLocalQueryExecutor)
that passed connection.url verbatim into pg, so file:/env: secret references
failed with "SASL: SCRAM-SERVER-FIRST-MESSAGE: client password must be a string".

Collapse onto the connector-based executor already used by MCP and ingest
(createKtxCliIngestQueryExecutor), which resolves secret references and supports
every driver. Delete the now-dead local/postgres/sqlite query executors, their
tests, and the orphaned hasLocalQueryExecutor driver flag.

* docs(agents): require one implementation per capability

Add a design-reasoning default and a matching self-check question telling agents
to route callers through a single shared implementation of a capability rather
than forking a parallel one, and to fix the shared layer rather than patch one
branch. Encodes the lesson from a divergent SQL-execution-path bug, stated
generally.

CLAUDE.md is a symlink to AGENTS.md, so both agent-instruction files are covered.

docs-site/content/docs/cli-reference/ktx-setup.mdx

@@ -54,7 +54,6 @@ prompts.
 | `--llm-backend <backend>` | LLM backend: `anthropic`, `vertex`, `claude-code`, or `codex` |
 | `--llm-backend claude-code` | Use the local Claude Code session for **ktx** LLM calls |
 | `--llm-backend codex` | Use local Codex authentication for **ktx** LLM calls |
-| `--llm-model <model>` | LLM model ID or backend model alias to validate and save |
 | `--anthropic-api-key-env <name>` | Environment variable containing the Anthropic API key |
 | `--anthropic-api-key-file <path>` | File containing the Anthropic API key |
 | `--vertex-project <project>` | Vertex AI project ID, `env:NAME`, or `file:/path` reference |
@@ -64,13 +63,9 @@ prompts.
 Choose only one Anthropic credential source. Anthropic credential flags are only
 valid with the Anthropic backend; Vertex flags are only valid with the Vertex
 backend. The `claude-code` and `codex` backends use local authentication instead
-of Anthropic API key or Vertex flags. For Claude Code, `--llm-model` accepts
-`sonnet`, `opus`, `haiku`, or a full Claude model ID. For Codex, `--llm-model`
-accepts `codex`, `default`, or a `gpt-*` / `codex-*` model ID such as
-`gpt-5.5`; any other value is rejected before the auth probe. Run `codex` to
-see the models available to your login, and pick a `gpt-*` / `codex-*` id from
-that list. Note that `*-codex` API-billing model IDs (for example
-`gpt-5.3-codex`) are not available to ChatGPT-subscription logins.
+of Anthropic API key or Vertex flags. After you choose a backend, `ktx setup`
+writes that backend's per-role model preset to `ktx.yaml`. To change a model,
+edit the matching `llm.models.<role>` value in `ktx.yaml`.
 
 ### Embeddings
 
@@ -198,14 +193,13 @@ ktx setup
 # Run setup for a specific project directory
 ktx setup --project-dir ./analytics
 
-# Use Claude Code with Opus for ktx LLM calls
+# Use Claude Code for ktx LLM calls
 ktx setup \
   --project-dir ./analytics \
-  --llm-backend claude-code \
-  --llm-model opus
+  --llm-backend claude-code
 
 # Configure **ktx** to use local Codex authentication for LLM work
-ktx setup --llm-backend codex --llm-model gpt-5.5 --no-input
+ktx setup --llm-backend codex --no-input
 ```
 
 When you choose `--llm-backend codex`, setup prints a warning if the public