[cleanup] clear radon C and deptry warnings on develop

[VGonPa]

Summary

Pure tech-debt cleanup. Clears the two warnings that survived on develop:

• Radon WARN — 3 grade-C functions refactored down to A/B
• Deptry WARN — 1 DEP003 false positive on the optional browser_cookie3 helper silenced

Behaviour unchanged. All 506 existing tests pass without modification — these are pure refactors plus a config tweak.

The four fixes

1. validate.validate_judgment C(16) → A(2) — split into focused sub-validators (_validate_judgment_keys, _validate_summary, _validate_topics_list, _validate_primary_topic). Top-level orchestrator just concatenates errors and keeps the early-return on non-list topics.
2. archive._archive_tweet_to_item C(11) → A(3) — extracted two substantive parsing helpers: _extract_archive_links (entities.urls navigation + domain derivation) and _extract_archive_media (extended/legacy media source selection + type normalisation + URL fallback).
3. generate._render_index C(13) → B(10) — extracted _count_topic_frequency (the only non-rendering logic — nested loop + dict mutation). Stat counters and markdown emission stay inline; that's the function's actual job.
4. pyproject.toml — added DEP003 = ["browser_cookie3"] to [tool.deptry.per_rule_ignores]. The helper is guarded by try/except ImportError in scripts/import_*_session.py and was already covered by DEP001; DEP003 surfaces on installs where the package gets pulled in via another extra. Comment updated to explain both. Chose the per-rule ignore over an [project.optional-dependencies] sessions group because the helper is install-on-demand and isn't part of the project's dependency surface.

Proof — scripts/check.sh SUMMARY

Before (develop)

  ✅ Ruff (linting)       PASS
  ✅ Ruff (format)        PASS
  ✅ Mypy (types)         PASS
  ⚠️  Radon (complexity)   WARN - Has grade C
  ✅ Bandit (security)    PASS
  ✅ Vulture (dead code)  PASS
  ✅ Interrogate (docs)   PASS - 84.0%
  ✅ Detect-secrets       PASS
  ✅ Tests                PASS - 506 tests
  ✅ Coverage             91%
  ⚠️  Deptry (deps)        WARN

After (this branch)

  ✅ Ruff (linting)       PASS
  ✅ Ruff (format)        PASS
  ✅ Mypy (types)         PASS
  ✅ Radon (complexity)   PASS - All A/B
  ✅ Bandit (security)    PASS
  ✅ Vulture (dead code)  PASS
  ✅ Interrogate (docs)   PASS - 84.9%
  ✅ Detect-secrets       PASS
  ✅ Tests                PASS - 506 tests
  ✅ Coverage             91%
  ✅ Deptry (deps)        PASS

Test plan

• uv run pytest — 506 passed (unchanged count)
• uv run ruff check src/ tests/ — All checks passed
• uv run ruff format --check src/ tests/ — clean
• uv run mypy --ignore-missing-imports src/ — no issues
• bash scripts/check.sh — ALL CRITICAL CHECKS PASSED, zero warnings
• Radon grade C count: 3 → 0
• Deptry findings: 2 → 0