fix(context): strip controls from provenance pointers

[SUaDtL]

Summary

• strip control, formatting, and line-separator characters from provenance document names, claim text, and line ranges before tier-4 context assembly
• suppress records whose document key becomes empty after sanitization
• keep canonical core and both shipped host copies byte-identical
• close task v2.harden.0002

Security posture

The sanitizer removes Unicode categories Cc, Cf, Zl, and Zp before pointer construction and before the 150-token budget is applied. Malformed values fail silent. Reviewers found an adjacent document-key path during the first pass; that path is covered by the same sanitizer in the final diff. Security, architecture, and coverage re-reviews report no remaining findings.

Verification

• 15 repository script suites passed
• 967 hook tests passed
• 192 read-injection tests passed
• sync-core --check passed for 42 core files across both plugin copies
• Python syntax checks passed for all three touched runtime copies
• plugin reference graph passed
• staged whitespace and secret scans passed

[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Superseded by #313, the single hackathon review surface.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.