Implement Stage 10 file and folder ingestion

[aarambh-darshan]

Summary

Implements Stage 10 file and folder ingestion for Manas.

What Changed

• Replaced the placeholder manas-ingest crate with a std-only ingestion pipeline.
• Added IngestSource::{RawText, File, Folder} and TextChunk with per-chunk source metadata.
• Added deterministic text normalization and bounded chunking with CHUNK_SIZE and CHUNK_OVERLAP.
• Added parsers for .txt, .md, .rs, .toml, .json, and .csv.
• Added recursive deterministic folder walking that skips unsupported files in folders.
• Added explicit unsupported-format errors for direct file inputs.
• Added Source display support for readable source metadata.
• Added Trainer::learn_with_source so file source metadata is attached to learned neurons.
• Wired manas teach <text|file|folder> [--recursive] through the CLI.
• Updated teach reporting to aggregate multi-chunk and multi-fact ingestion.
• Updated README, ROADMAP, CHANGELOG, and ARCHITECTURE for Stage 10 completion.

Tests

• cargo test -p manas-ingest -p manas-cli -p manas-store
• cargo test -p manas-learn anti_forgetting
• cargo test --workspace
• git diff --check

Notes

Stage 10 is now complete. Stage 11, importance scoring and promotion, is marked as next in the docs.