fix(provenance): confine paths before hashing

[SUaDtL]

Summary

• Reject NUL, CR/LF, POSIX and Windows absolute paths, root-self paths, parent traversal, and existing symlink escapes before provenance entries reach git hash-object.
• Remove rejected entries from the in-memory drift comparison so invalid records cannot create false missing-file warnings.
• Add regression coverage for every rejected path class while preserving valid batched hashing and byte-identical ca and ca-codex hook copies.
• Mark backlog task v2.harden.0001 complete through the sanctioned task lifecycle.

Why

Provenance records are repository data. They must not control Git's newline-delimited path protocol or resolve outside the project root during SessionStart drift checks.

Verification

• python .github/scripts/test_provenancelib.py (109 tests)
• Exact tech-stack.md project suite (15 script suites plus 967 hook tests)
• python -m py_compile for all three touched hook copies
• python tools/sync-core.py --check
• python .github/scripts/check-plugin-refs.py
• Security review: PASS, no findings
• Coverage review: PASS after adding the symlink-escape fixture
• Architecture-drift review: PASS

Tradeoff

Conflict level: §2 L1. The existing Git-based hashing design retains a narrow validation-to-open race under a concurrent local filesystem mutator. The documented boundary assumes a cooperative local host, and descriptor-based hashing would be a separate architecture change.

[SUaDtL]

Superseded by #313, the single hackathon review surface. This PR's recorded head and changes are represented in #313's exact 16-PR / 29-commit / 126-path source manifest. PR #313 passed final exact-head CI at commit 6173b1d and remains open and unmerged. Closing this source PR to avoid parallel review; please continue review and discussion on #313.