add markdown linting and cut AGENTS.md back to rules

AGENTS.md was a per-module tour of the code, which restated what the code says
and had already drifted: it described the example as emitting three inputs when
it emits five. It is now the conventions an agent cannot infer -- dora version,
uv, ruff, numpy docstrings, the platform requirement, act, and what not to do --
and nothing else. The gotchas it carried are explained at their point of use in
the code instead.

pymarkdown lints the markdown, configured in pyproject.toml and run in CI
beside ruff. It caught a fenced block with no language and an over-long table
row. ruff's pydocstyle convention moves to numpy.

GEMINI.md is removed.

README.md

@@ -74,7 +74,7 @@ and it is what makes a wiring mistake fail at build time instead of at runtime.
 example source is typed inline in the dataflow with `output_types:`, so `dora validate`
 checks the two against each other:
 
-```
+```text
 $ dora validate dataflow.yml
   node "view": injected 4 contract type(s) from .../dora-node.yml
 All type annotations OK.
@@ -113,7 +113,7 @@ no window. That is what makes it safe to run in a pipeline test.
 |---|---|---|
 | `image` | `std/media/v1/Image` struct | none — the struct describes itself |
 | `depth` | `std/media/v1/Image` struct, one channel | `units` (defaults to `mm`) |
-| `camera_info` | Flat `Float32` array, `[fx, fy, cx, cy]` or a 9-element K | `distortion`, `distortion_model` |
+| `camera_info` | `[fx, fy, cx, cy]` or a 9-element K | `distortion`, `distortion_model` |
 | `bbox` | Arrow struct array, element `[0]` with fields `bbox`, `conf`, `labels` | `format` |
 | `text` | Arrow array of size 1 | — |