fix(cli): Add help recipe for the detect command

`detect` is a registered subcommand, so it appeared in the `taskless help`
topic index — but `taskless help detect` had no backing `detect.txt` and fell
through to "Unknown command", exiting 1. Every other registered command already
had a matching help file; `detect` was the lone gap.

Add `detect.txt` documenting the `--json` output shape (linters, languages,
ruleStyles) and cross-linking to the route/existing authoring flow that consumes
those signals.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: thecodedrift

.changeset/detect-help-topic.md

@@ -0,0 +1,12 @@
+---
+"@taskless/cli": patch
+---
+
+Add a help recipe for the `detect` command.
+
+`detect` is a registered subcommand, so it appeared in the `taskless help`
+topic index — but `taskless help detect` had no backing `detect.txt` and fell
+through to "Unknown command", exiting 1. Every other registered command already
+had a matching help file; `detect` was the lone gap. The new recipe documents
+the `--json` output shape (linters, languages, ruleStyles) and cross-links to
+the `route`/`existing` authoring flow that consumes it.

packages/cli/src/help/detect.txt

@@ -0,0 +1,64 @@
+# Topic: detect     (CLI v%(CLI_VERSION)s / topic v1)
+
+## Goal
+Scan the working directory for the linters it configures, the
+languages it uses, and the styles of any rules the repo already
+authors. Offline and deterministic — no network, no auth, no state
+change. This is the discovery step that feeds rule-authoring: the
+routing flow reads `detect` to decide where a new rule should live.
+
+## Preconditions
+- None. Works in any directory; doesn't require `.taskless/`.
+
+## Steps
+
+1. **Invoke the CLI** with JSON output:
+   ```
+   npx @taskless/cli detect --json
+   ```
+
+2. **Parse the response.** Shape:
+   ```json
+   {
+     "success": true,
+     "linters": [
+       {
+         "name": "eslint",
+         "evidence": ["eslint.config.js", "dependency eslint (package.json)"]
+       }
+     ],
+     "languages": ["typescript", "javascript"],
+     "ruleStyles": [
+       {
+         "source": ".taskless/rules",
+         "description": "ast-grep rules with YAML metadata sidecars"
+       }
+     ]
+   }
+   ```
+   - `linters` — each has a `name` and `evidence` (config-file paths,
+     a pyproject table marker, or a dependency marker from the
+     language's package file; not every entry is a path).
+   - `languages` — inferred from manifests and the detected linters.
+   - `ruleStyles` — how the repo authors its own rules, surfaced for
+     downstream reuse.
+
+3. **Use the signals to route.** Feed the output into rule authoring:
+   - A detected linter the repo already uses → author the rule there
+     (`taskless help existing`).
+   - No suitable linter, local-only → `taskless help static`.
+   - See `taskless help route` for the full decision.
+
+## Errors
+
+When `--json` is set, failures emit `{ ok: false, code, message }`:
+
+| code              | meaning                          | fix                       |
+|-------------------|----------------------------------|---------------------------|
+| `INTERNAL_ERROR`  | Internal schema validation       | Report; likely a CLI bug  |
+
+## See Also
+
+- `taskless help route` — decide where to author a rule from these signals
+- `taskless help existing` — author a rule in a linter the repo already uses
+- `taskless help check` — run rules against the codebase