Limit source supplements and freeze fresh precision controls

[Sahith59]

The first paid source-supplement screen moved the frozen 150-pair slice from 70 to 87 correct, but it failed the prospective control floor by one case (55/58 versus 56), so this change keeps the broad candidate blocked.

This PR adds a precision-limited successor that ranks the complete scoped source before filtering, applies a fixed lexical threshold, and returns at most five complete turns. On the authoritative offline audit it reduces added turns from 4,190 to 652 (84.44%), restores 138 annotated turns with zero annotated loss, and reaches 24 of the 72 persistent-miss questions. The next frozen screen keeps all 30 abstentions while replacing all 40 prior non-abstention controls with deterministic type-balanced controls.

Validation:

• 66 focused tests pass
• independent 500-packet precision audit passes
• independent selection verification passes with zero prior non-abstention control overlap
• both complete network-denied synthetic scenarios pass, including zero-call resume
• no paid execution, QA claim, default promotion, or full-500 run is included

Exact proposed package: cd80a0168802bb1db70fb486902a497539b9cd683de41e6062aace774eae8d9e, capped at $8.86 and at most 600 provider calls. Paid execution requires separate founder approval.