docs: document weekend PRs #466/#494/#495 + Stage C full-catalog completion

[WilfordGrimley]

Covers five undocumented items from the 2026-07-25/26 weekend:

PR #494 — local_calculate_verdicts observability additions (docs/features/stage-e-operations.md)

• --diff-report PATH: per-card JSONL of would-act-on cards, stream-written, lifts audit cap to sys.maxsize
• Per-calculator counters in PilotRunLedger (counters["join_key"], ["fallback"], ["slow_path"]), each with considered/would_cast/votes_written/already_voted/skip_counts
• Counters-before-output discipline (fixes the counters={} severed-stdout incident on run 20260726T165343-3e8301db)

PR #495 — rejudge_fallback_channel compare-and-retract (docs/features/stage-e-operations.md)

• New MPCAutofill/cardpicker/management/commands/rejudge_fallback_channel.py
• Re-derives stage-d-fallback-v1 conclusions from current ImageEvidence (zero image fetches), retracts rows where conclusion changed
• Safety gate, flags, counters, two-step runbook documented

Stage C full-catalog completion record (docs/reports/2026-07-26-stagec-full-catalog-completion.md, docs/reports/README.md, docs/pipeline-fidelity-gate.md)

• 218,108/218,516 cards (99.8%), runs pass-full-20260725 + -r2 (supersede all prior Stage C last-writer rows)
• 1,614 fetch_ok=False rows + 408 cards with no evidence (all Google Drive)
• Stage C run history table in pipeline-fidelity-gate.md §6 updated to current state

PR #466 — web-ci.yml per-surface CI gating (docs/infrastructure.md)

• changes job, two surfaces (backend/frontend), fallback logic, removed duplicate test-pre-commit job

PR #477 — md5_checksum substrate: no doc gap found — already covered in docs/federation-v1.md and docs/features/stage-e-operations.md.

Wiki checklist: stage-e-operations.md and infrastructure.md are wiki-published — wiki regenerates on next master push touching docs/**.