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/__init__.py

@@ -0,0 +1 @@
+"""Package marker so `python3 -m unittest Tools.tests.<module>` resolves."""