feat: implement AtoCore Phase 0 + Phase 0.5 (foundation + PoC)

Complete implementation of the personal context engine foundation:
- FastAPI server with 5 endpoints (ingest, query, context/build, health, debug)
- SQLite database with 5 tables (documents, chunks, memories, projects, interactions)
- Heading-aware markdown chunker (800 char max, recursive splitting)
- Multilingual embeddings via sentence-transformers (EN/FR)
- ChromaDB vector store with cosine similarity retrieval
- Context builder with project boosting, dedup, and budget enforcement
- CLI scripts for batch ingestion and test prompt evaluation
- 19 unit tests passing, 79% coverage
- Validated on 482 real project files (8383 chunks, 0 errors)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/atocore/api/routes.py

@@ -0,0 +1,132 @@
+"""FastAPI route definitions."""
+
+from pathlib import Path
+
+from fastapi import APIRouter, HTTPException
+from pydantic import BaseModel
+
+from atocore.context.builder import (
+    ContextPack,
+    build_context,
+    get_last_context_pack,
+    _pack_to_dict,
+)
+from atocore.ingestion.pipeline import ingest_file, ingest_folder
+from atocore.retrieval.retriever import retrieve
+from atocore.retrieval.vector_store import get_vector_store
+
+router = APIRouter()
+
+
+# --- Request/Response models ---
+
+
+class IngestRequest(BaseModel):
+    path: str  # file or folder path
+
+
+class IngestResponse(BaseModel):
+    results: list[dict]
+
+
+class QueryRequest(BaseModel):
+    prompt: str
+    top_k: int = 10
+    filter_tags: list[str] | None = None
+
+
+class QueryResponse(BaseModel):
+    results: list[dict]
+
+
+class ContextBuildRequest(BaseModel):
+    prompt: str
+    project: str | None = None
+    budget: int | None = None
+
+
+class ContextBuildResponse(BaseModel):
+    formatted_context: str
+    full_prompt: str
+    chunks_used: int
+    total_chars: int
+    budget: int
+    budget_remaining: int
+    duration_ms: int
+    chunks: list[dict]
+
+
+# --- Endpoints ---
+
+
+@router.post("/ingest", response_model=IngestResponse)
+def api_ingest(req: IngestRequest):
+    """Ingest a markdown file or folder."""
+    target = Path(req.path)
+    if target.is_file():
+        results = [ingest_file(target)]
+    elif target.is_dir():
+        results = ingest_folder(target)
+    else:
+        raise HTTPException(status_code=404, detail=f"Path not found: {req.path}")
+    return IngestResponse(results=results)
+
+
+@router.post("/query", response_model=QueryResponse)
+def api_query(req: QueryRequest):
+    """Retrieve relevant chunks for a prompt."""
+    chunks = retrieve(req.prompt, top_k=req.top_k, filter_tags=req.filter_tags)
+    return QueryResponse(
+        results=[
+            {
+                "chunk_id": c.chunk_id,
+                "content": c.content,
+                "score": c.score,
+                "heading_path": c.heading_path,
+                "source_file": c.source_file,
+                "title": c.title,
+            }
+            for c in chunks
+        ]
+    )
+
+
+@router.post("/context/build", response_model=ContextBuildResponse)
+def api_build_context(req: ContextBuildRequest):
+    """Build a full context pack for a prompt."""
+    pack = build_context(
+        user_prompt=req.prompt,
+        project_hint=req.project,
+        budget=req.budget,
+    )
+    pack_dict = _pack_to_dict(pack)
+    return ContextBuildResponse(
+        formatted_context=pack.formatted_context,
+        full_prompt=pack.full_prompt,
+        chunks_used=len(pack.chunks_used),
+        total_chars=pack.total_chars,
+        budget=pack.budget,
+        budget_remaining=pack.budget_remaining,
+        duration_ms=pack.duration_ms,
+        chunks=pack_dict["chunks"],
+    )
+
+
+@router.get("/health")
+def api_health():
+    """Health check."""
+    store = get_vector_store()
+    return {
+        "status": "ok",
+        "version": "0.1.0",
+        "vectors_count": store.count,
+    }
+
+
+@router.get("/debug/context")
+def api_debug_context():
+    """Inspect the last assembled context pack."""
+    pack = get_last_context_pack()
+    if pack is None:
+        return {"message": "No context pack built yet."}
+    return _pack_to_dict(pack)