docs: add Batch 1 Turkish lexicon research scaffold (PR2a)

[aerbilir]

Summary

Adds the Batch 1 Turkish lexicon research and curation document scaffold for v0.4 PR 2. This is structure and workflow only — no candidate research, dictionary changes, or corpus changes.

Changes

• Creates docs/batch1-tr-lexicon-research.md with:
  • Purpose, scope, and research discipline
  • Planned agent-reach research contexts (no results yet)
  • Empty Stage 1 candidate pool table (~30–40 candidates)
  • Empty Stage 2 maintainer evaluation table
  • Empty Stage 3 Approved Batch 1 table (exactly 15 entries required before PR 3)
  • Empty deferred and rejected candidate tables
  • PR 3 readiness checklist
• Updates CHANGELOG.md under [Unreleased]

Out of scope (this PR)

• agent-reach research execution
• Candidate terms
• data/tr.php changes
• Corpus fixture changes
• Matcher, dictionary infrastructure, or public API changes

Validation

• composer validate ✅
• composer test ✅

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