feat(ingestion): add DOCX/CSV/XLSX parsing and fixed-size chunking (ADR-0018)

Adds src/application/ingestion/ -- Persian normalization, DOCX body
walk with structural data/layout table classification, CSV/XLSX row
rendering, and fixed-size token chunking (cl100k_base, 400/60/512) --
as pure functions per ADR-0015, tested against real production
documents (asia_data_sample, kept out of the repo). ADR-0018 records
where this diverges from ADR-0004 (fixed-size default, no invented
headings/tree, structural table classification, header-provable
labeling only). Plan 001's scope line is corrected from CSV-only to
DOCX/XLSX/CSV, and CLAUDE.md's stale project-status paragraph is
updated to match current implementation state.

.env.example

@@ -44,3 +44,17 @@ INGESTION_EMBED_CONCURRENCY=4
 # Qdrant
 QDRANT_URL=http://127.0.0.1:6343
 QDRANT_API_KEY=
+
+# Parsing and chunking (ADR-0018).
+# max_chunk_tokens is nomic-embed-text-v2-moe's sequence length; text past it
+# is silently truncated by the model, so the cap is enforced before embedding.
+# chunk_size sits under it to leave room for the `search_document: ` prefix.
+CHUNKING_STRATEGY=fixed_size
+CHUNKING_CHUNK_SIZE=400
+CHUNKING_CHUNK_OVERLAP=60
+CHUNKING_MAX_CHUNK_TOKENS=512
+CHUNKING_ENCODING_NAME=cl100k_base
+
+# tiktoken downloads its vocabulary on first use; point this at a
+# pre-populated directory for offline/air-gapped deployments.
+# TIKTOKEN_CACHE_DIR=