feat(prose-redaction): native AI-writing-tell inventory for generated prose

[cdeust]

Implements #166 — the redaction mechanism as a native Cortex capability, no cross-repo dependency (the agent-surface implementation lives independently in zetetic-team-subagents).

What

1. mcp_server/core/prose_redaction.py (pure core, stdlib-only) — the mechanical inventory with per-pattern # source: annotations (Wikipedia "Signs of AI writing" / WikiProject AI Cleanup; house rules): em dashes (zero-tolerance policy for generated copy), banned vocabulary, weasel attribution (escalated to a violation by the project's own zetetic standard), and trailing -ing tack-on analyses (narrow verb set, near-zero false positives on technical prose). scan_prose() skips fenced code, scans frontmatter (titles are reader-facing). REDACTION_CONVENTIONS is the prompt-time block.
2. Authoring prompts — all three auto-curator templates (authoring, coverage, re-author) now carry the redaction conventions, so pages avoid the tells at generation time.
3. wiki_write — advisory redaction_findings summary (count, by-category, first 10 with line + excerpt) on every written page; never blocks; omitted when clean. Generated prose gets measured at the exact point it becomes durable.

Tests

13 new tests: every pattern class, the false-positive guard (ordinary participle clauses stay silent), fence/frontmatter behavior, summary shape, and an integration check that all three prompts carry the conventions. One meta-result worth recording: the eval initially failed because the conventions block itself contained an em dash — caught by its own test.

Affected suites green locally: prose_redaction 13/13, wiki_write 16/16, auto_curator/curate_wiki 9/9. ruff check + format clean.

Done criteria from #166

• Inventory carries per-pattern sources: done.
• Conventions in wiki authoring paths: done (all three prompt templates).
• Write-time measurement: done (redaction_findings).
• Remaining (follow-up): regenerated before/after anchor page, and the week-of-autonomous-cycle zero-hits observation — both need live wiki cycles, not code.

Closes #166 (code half).

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