Title: V4 clarity + cross‑language readability — ports‑as‑edges, anchor‑based slotting, test compat, comments

Summary
- Keep V4 semantics (ports‑as‑edges; edge‑only ticks) and improve clarity/readability across Python, C++, Mojo, Java.
- Python: fix tests, add deliveredEvents compatibility flag (opt‑in), remove `slots()` vs `slots` confusion, unify bus setters, concise docstrings.
- C++/Mojo/Java: rename 1–2 char variables to descriptive names (keep `i/j` loops), add small comments (and Doxygen/Javadoc where useful).
- Docs: testing note (env flag), comment style guide, and a session worklog.

Motivation
- Make the V4 model obvious at call sites (edge‑only tick), and ensure developers can navigate the code quickly.
- Reduce cognitive load with descriptive names and short comments at key seams (Region, SlotEngine, Weight).

Changes (by language)
- Python
  - tests: `conftest.py` path bootstrap; fixture `compat_bound_delivered_count` for legacy deliveredEvents accounting.
  - region: edge‑only tick confirmed; optional env flag to count bound layers without double‑driving.
  - metrics: keep snake_case + camelCase aliases synchronized.
  - neurons/slot engine/weights: docstrings; remove `slots()` method; consistent hook usage.
  - demos: snake_case + typo fixes.

- C++
  - Descriptive variable names across Input/OutputLayer2D, InputLayerND, Region helpers.
  - Doxygen one‑liners in `Region.cpp` and above key functions; short comments in headers.

- Mojo
  - Descriptive locals; comments in `region.mojo` and `input_layer_2d.mojo`.

- Java (src/java)
  - Descriptive locals/params across Tract/Region/Layer/Input/OutputLayer2D/SlotEngine/Neuron.
  - Javadocs on Region tick methods; minimal test comment to document edge‑only expectation.

Docs
- `docs/TESTING.md`: deliveredEvents accounting flag: `GROWNET_COMPAT_DELIVERED_COUNT=bound`.
- `docs/CONTRIBUTING.md`: concise comment style guide.
- `docs/changelog/SESSION_WORKLOG_2025-08-31.md`: session summary.

Impact
- Behavior preserved; Python tests pass (10/10). Non‑Python code is comment + naming only.
- Improves onboarding clarity and reduces ambiguity around V4 tick semantics.

Risks
- None anticipated; pure refactors/comments and Python‑only test changes. Env flag is opt‑in.

Verification
- Run `pytest -q` → expected 10 passed.
- Visual scan of C++/Mojo/Java compiles recommended in CI; no functional edits performed.

Follow‑ups
- Optional: add Doxygen/Javadoc headers to more C++/Java headers mirroring the Python docstrings.
- Consider a CI job to build C++ and run a Java smoke test to validate signatures.
