docs: add phases, tasks, and chunking strategies documentation

Why:
- Need implementation plan and task tracking documentation
- Need strategy explanations for reference

Changes:
- phases.md: 5-phase implementation plan with status tracking
- tasks.md: 25 tasks mapped to phases and steps
- chunking_strategies.md: detailed explanations of all 5 strategies

docs/phases.md

@@ -0,0 +1,115 @@
+# Phases & Steps
+
+Implementation plan for the RAG Chunking Strategy Benchmarking Framework.
+Each step maps back to tasks in [tasks.md](tasks.md).
+
+---
+
+## Phase 1: Document Parsing + Storage
+
+Foundation layer. Everything else depends on this.
+
+| Step | What | Files | Status |
+|------|------|-------|--------|
+| 1 | SQLite Storage Layer | `src/storage/sqlite.py` | DONE |
+| 2 | Qdrant Storage Layer | `src/storage/qdrant.py` | DONE |
+| 3 | Document Parser | `src/documents/parser.py` | DONE |
+| 4 | Document Routes + Service | `src/documents/routes.py`, `src/documents/service.py`, `src/documents/models.py` | DONE |
+
+**Endpoints delivered:**
+- `POST /documents` — upload .docx
+- `POST /documents/{id}/process` — run strategies (stubbed)
+- `DELETE /documents/{id}` — remove document + vectors
+- `GET /strategies` — list all 5 strategies
+
+---
+
+## Phase 2: Chunking Strategies
+
+The core evaluation targets. Each strategy is an independent module.
+
+| Step | What | Files | Status |
+|------|------|-------|--------|
+| 5 | Base Strategy Interface | `src/chunking/base.py` | TODO |
+| 6 | Five Strategy Implementations | `src/chunking/strategies/recursive.py`, `markdown_structure.py`, `semantic.py`, `parent_child.py`, `contextual_structure.py` | TODO |
+| 7 | Embedding Service | `src/chunking/embedding.py` | TODO |
+| 8 | Chunking Orchestration | `src/chunking/service.py` | TODO |
+
+**ADR alignment:**
+- ADR 0001: Unified Chunk model (nullable fields)
+- ADR 0002: Hard-fail on contextual enrichment failure
+- ADR 0003: Per-strategy failure isolation
+- ADR 0005: Hardcoded article-level parents
+- ADR 0011: Embed full enriched text for contextual
+- ADR 0012: Sentence-level semantic with min chunk size
+- ADR 0013: Leaf-level markdown chunks only
+- ADR 0015: Direct API usage, no LangChain/LlamaIndex
+
+**Delivers:** The `POST /documents/{id}/process` endpoint goes from stub to real — chunking, embedding, and Qdrant storage for all 5 strategies.
+
+---
+
+## Phase 3: Query Pipeline
+
+Retrieval + generation. The bridge between storage and evaluation.
+
+| Step | What | Files | Status |
+|------|------|-------|--------|
+| 9 | Query Service | `src/benchmarking/query_service.py` | TODO |
+| 10 | Query Routes | `src/benchmarking/routes.py` | TODO |
+
+**Endpoints delivered:**
+- `POST /queries` — ask a question against a strategy
+- `GET /queries/{id}` — retrieve past query
+
+**Pipeline:** question → embed → vector search (Qdrant) → top_k chunks → gpt-4o-mini → answer + metadata.
+
+---
+
+## Phase 4: Benchmarking + Evaluation
+
+The reason the project exists. Compare strategies head-to-head.
+
+| Step | What | Files | Status |
+|------|------|-------|--------|
+| 11 | LLM-as-Judge Evaluation | `src/benchmarking/evaluation.py` | TODO |
+| 12 | Benchmark Service | `src/benchmarking/benchmark_service.py` | TODO |
+| 13 | Benchmark Routes | extends `src/benchmarking/routes.py` | TODO |
+| 14 | HTML Report Template | `src/benchmarking/templates/report.html` | TODO |
+
+**Endpoints delivered:**
+- `POST /benchmarks` — run benchmark (single or dataset)
+- `POST /benchmarks?dry_run=true` — cost estimate only
+- `GET /benchmarks/{id}` — retrieve experiment results
+- `GET /benchmarks/{id}/report` — download HTML report
+
+**Evaluation metrics (ADR 0004):**
+- Context Relevance (1–10)
+- Answer Similarity (1–10)
+- Faithfulness (1–10)
+- Hallucination (bool)
+
+**Modes:**
+- Single question
+- Dataset (questions.json)
+- Dry run (cost estimation)
+
+---
+
+## Phase 5: Wiring + Verification
+
+Polish, integration, and proof that it all works end-to-end.
+
+| Step | What | Files | Status |
+|------|------|-------|--------|
+| 15 | Wire All Routers + Logging | `src/main.py` | TODO |
+| 16 | End-to-End Smoke Test | test suite | TODO |
+
+**Verification checklist:**
+- Upload insurance .docx
+- Process with all 5 strategies
+- Ask 3 test questions
+- Run mini benchmark (3 questions × 5 strategies)
+- Verify HTML report renders
+- Confirm per-strategy failure isolation (simulate one strategy failure)
+- Confirm dry-run cost estimation matches actual cost within 10%