Review fixes F3–F5 and rebuild flags

• F3 (one disclosed contract revision, dred.py). The opaque $d$ now refuses {expr.replace(d,$\cdot$)}, pattern matching on $d$ and the lambdify/code-printer paths outside substitute_d. Paths without a hook (callable-query replace, Poly.eval, string round trips) are excluded by a static AST scan. The P13–P15 certificate values are unchanged against the p15 reference values.

• F4. The page footer comes from one version variable. The PDF readback also covers the D13, Batch A, Batch C and E2 value blocks.

• F5. Every changed file, contract and non-contract, is listed in change_log_vs_p15 of the release status.

independent_rebuild_passed_p15=true is bound to the p15 tree 79f53752{} and zip 54325c1f{} (same box). The p16 tree's own independent rebuild is pending.