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.

src/application/ingestion/errors.py

@@ -0,0 +1,41 @@
+"""Errors raised by the parsing and chunking pipeline (ADR-0018).
+
+These carry no HTTP knowledge — the API layer maps them to status codes
+(ADR-0015: `application/` contains no FastAPI request objects).
+"""
+
+
+class IngestionError(Exception):
+    """Base class for ingestion failures."""
+
+
+class DocumentParseError(IngestionError):
+    """A source file could not be decoded, opened, or yielded no text.
+
+    Maps to `400` per ADR-0017 ("unparseable file → 400").
+    """
+
+
+class UnsupportedSourceTypeError(IngestionError):
+    """A source file's type is not ingestible in this version.
+
+    Maps to `415`. `.doc` lands here until an out-of-process conversion
+    service exists (ADR-0018).
+    """
+
+
+class ChunkLimitExceededError(IngestionError):
+    """A document produced more chunks than `INGESTION_MAX_CHUNKS_PER_FILE`.
+
+    Maps to `413` per ADR-0017.
+    """
+
+
+class ChunkTooLargeError(IngestionError):
+    """A chunk exceeded the embedding model's sequence length.
+
+    This is an internal invariant violation, not a user error: the splitter is
+    supposed to make it impossible. It exists because the failure it guards
+    against is silent — `nomic-embed-text-v2-moe` truncates over-long input
+    without raising (ADR-0004).
+    """