Harden project compatibility inspection snapshots

[Deicyde]

Follow-up to merged #14.

Summary

• certify a Lean/Mathlib release pair only after strictly decoding the active
  Lake TOML requirement and every Lake-consumed manifest/override field
• read the small decision-file set as one coherent bounded snapshot, including
  presence, exact-case aliases, root discovery, and .lake generation checks;
  retry boundedly and fail if the project changes
• open decision files nonblocking and no-follow where supported, require a
  regular descriptor before reading, cap bytes, and revalidate descriptor,
  pathname, and content afterward
• preserve Add bounded Lean project inspection #14's slim public JSON/model surface and exact-only optional
  Autoform scaffold detection

This closes three reproduced false-safety gaps from the merged implementation:
a malformed Lake field could still report supported; sequential reads could
synthesize a supported pair that never existed; and a regular-file-to-FIFO swap
could be opened after the pathname check.

Validation

• tests/test_project_inspect.py: 169 passed on Python 3.10
• tests/test_project_inspect.py: 169 passed on Python 3.13
• combined project/plugin/CLI focused gate: passed
• full Ruff and git diff --check: passed
• make check-example: passed
• wheel build + isolated installed project inspect|versions: passed
• real formal-math, hatcher-at, and zeta7-irrational: correct unlisted
  current pairs
• real Lake 4.32.2 catalog sample: supported
• independent Lake-semantics and snapshot-race audits: approved

The unrelated full-suite subprocess tail and shared-.venv race were not used
as evidence; their affected paths are outside this three-file diff.

[Deicyde]

Superseded by #79 at the exact same commit 2d083e0. Development has been moved to a branch in facebookresearch/autoform-bot; the fork branch is being removed.