docs(agents): tooling-improvement and architecture-upkeep rules; add tool tests

Researched the sibling project's tooling discipline (tools/README inventory,
tools/tests with stdlib unittest, check_docs gate, clean-worktree rule, paid-API
tools human-triggered) and encoded it for this repository:

AGENTS.md gains two sections.
- 'Python and shell tooling': fix the tool not the artefact; improve over fork;
  one script one job; fail loudly; result files for Unreal commandlets; absolute
  paths into sandboxes; clean worktree for generators (.blend/.umap are
  read-only on checkout); network/paid tools human-triggered with 429 back-off;
  measure don't assert; document every tool in the README inventory; test the
  pure parts.
- 'Architecture documentation': Docs/Architecture is arc42 in Markdown; a table
  mapping each kind of change to the section that must be updated; describe what
  exists, ADRs append-only, keep architecture.md in sync, prettier --check.

Made the referenced scaffolding real rather than aspirational:
- Tools/tests/ (README + __init__) with 12 passing unittest tests covering
  input_emulation's ioctl/key-code encoding and block_height_report's height
  classification.
- requirements-tools.txt (requests).
- Extracted classify_height() out of block_height_report.main() so the roof/
  shelter rule is testable — the rule itself came from the v0.1.2 finding.
- Tools/README: tests section, input-injection rows, and the removed TEMP-QA row
  replaced by the real cvar/self-test description.
- Docs/Architecture 05 + architecture.md: tools table extended (input injection,
  tests) and a link to the tool rules; kept in sync per the new rule.

Tools/tests/README.md

@@ -0,0 +1,26 @@
+# Tooling tests
+
+Standard-library `unittest` tests for the host-side tools in `Tools/`. They never start Blender, Unreal, or the game; anything that needs those processes is verified by the tool itself and recorded in `Docs/release-checks.md` instead.
+
+Run from the repository root:
+
+```bash
+python3 -m pip install -r requirements-tools.txt
+python3 -m unittest discover -s Tools/tests -t Tools -p 'test_*.py'
+```
+
+The `-t Tools` top-level directory is required: the tests import the tool modules by their plain names (`import input_emulation`), which is why `Tools/tests/` carries an `__init__.py`.
+
+Individual test:
+
+```bash
+python3 -m unittest Tools.tests.test_input_emulation -v
+```
+
+## What belongs here
+
+Test the **pure** parts — argument parsing, key/coordinate encoding, geometry maths, licence gating, report formatting, decision classification. Network, Blender and Unreal calls stay out: a test that needs a paid API, a display, or an engine process is a manual check, not a unit test.
+
+When a tool's logic is buried in `main()`, extract it into a function so it can be tested directly. That is a tooling improvement, not test scaffolding.
+
+Geo (`Geo/tools/`) and Blender (`Art/blender/*/`) builders are tested the same way once their pure parts are extracted; note the module path in the test.