Add Vale prose checks for Python comments and docstrings

[MrC8559]

Summary

Completes the prose half of #61 with Vale, building on the identifier-name work merged in #74.

• checks Python comments plus module/class/function docstrings through a tree-sitter View;
• leaves ordinary Python string literals alone;
• adds two small project-owned advisory rules: plain-word substitutions and sentences over 30 words;
• wires Vale into the default prose gate/category;
• packages and hoists the Vale config/styles during harness init;
• installs pinned Vale 3.22.0 in the existing Ubuntu/macOS/Windows CI matrix;
• reports the rule and file/line location in actionable language.

Plain-English boundary

These are LoopGate's own advisory plain-English rules. This change:

• ships no ASD word list;
• does not claim ASD-STE100 conformance or certification;
• keeps each rule mechanical and easy to explain.

Tests

Added focused regression coverage proving that:

• module, class, and function docstrings are checked;
• comments are checked;
• ordinary string literals are not treated as prose;
• a sentence over 30 words is reported once;
• two separate shorter sentences are not incorrectly combined;
• the Vale config/style files are included in the installed harness.

Validation

The exact 14-file implementation was validated in the fork before this clean one-commit branch was created.

Final fork workflow run #20 passed completely on Ubuntu, macOS, Windows, and dependency review. The gate included Vale plus the repository's existing audit, security, pytest/100%-coverage, Pyright, Ruff format/lint, Pylint, and complexity checks.

Running the prose gate across the repository produced 12 advisory sentence-length warnings in 18 Python files and no errors. The detailed output is posted on #61 as requested.

Closes #61