Fix PR lens review: inline comments + split confidence thresholds

The "EvalOps PR lens review" system published 0 findings across the last
12 scheduled runs (~70 lens reviews) yet reported success every time.
Three bugs combined to make it silently green:

1. One blunt threshold (DEFAULT_MIN_CONFIDENCE = 0.82) decided both what
   to show a human and what fails the status, so real medium-confidence
   findings (0.6-0.8) were silently discarded.
2. Findings posted as one issue comment at the bottom of the PR with
   `path:line` as plain text, despite every finding carrying an exact
   code_location.
3. normalize_finding silently returned nil for malformed findings.

Changes:
- Publish as a single PR review (POST pulls/{pr}/reviews, event COMMENT)
  with inline comments anchored to each finding's code_location.
  meta-review parses each file's patch hunks to compute the set of
  addable right-side line numbers; findings whose path:line is in that
  set are inlined, the rest are folded into the review summary body
  (avoids GitHub's 422 on off-diff lines).
- Split the threshold in two: comment_min_confidence (default 0.55,
  env PR_LENS_COMMENT_MIN_CONFIDENCE) for surfacing; block_min_confidence
  (default 0.80, env PR_LENS_BLOCK_MIN_CONFIDENCE) for failing the
  status, and only on P0/P1. PR_LENS_MIN_CONFIDENCE / --min-confidence
  kept as a back-compat alias mapping to the block threshold.
- Honest green status: "N lenses · 0 findings >= 0.55" instead of
  implying nothing was found.
- normalize_finding now raises DroppedFinding; the caller counts and
  warns per dropped finding and records dropped_findings in the ledger.
- Idempotency preserved: prior marker issue-comment and prior marker
  inline review comments are deleted before posting, so re-running on
  the same head replaces rather than duplicates.
- Workflow gains comment_min_confidence / block_min_confidence inputs
  and keeps min_confidence for back-compat.

Test Plan:
- ruby -Itest -e 'ARGV.each { |path| require "./#{path}" }' test/*_test.rb
  => 125 runs, 1016 assertions, 0 failures, 0 errors, 0 skips
- New coverage: diff-hunk line parsing, inline-vs-summary split, the two
  thresholds, idempotent replacement, dropped-finding logging.

Rollback: revert this commit; behavior returns to the single-threshold
issue-comment publisher. No state migration involved.

Signal: 12 consecutive green scheduled runs with 0 published findings
(gh run list evalops-pr-lens-review.yml, 2026-06-08..09).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: haasonsaas