[lore 6/7] Ingester + heuristic classifier (Path B)

[kunallanjewar]

Summary

• Adds pkg/lore/ingest: Ingester interface, Result/FileError types, WalkDir filesystem walker, ChunkFile markdown chunker (H1/H2/H3 boundaries with YAML front matter)
• Adds pkg/lore/ingest/heuristic: NewIngester with four-level classification (front matter > path rules > heading patterns > fallback=research), DefaultRules table covering ADR/runbook/concept/reference/agent-config patterns, functional options WithRules/WithLogger/WithTracer/WithMaxFileSize
• OTel spans: lore.ingest.process (path.count, entries.count attrs) and lore.ingest.classify (per-file)
• Testdata corpus (5 fixture files) and 9 tests covering all classification paths, walker skip behavior, chunker boundaries, and per-file error handling without aborting the walk
• README updated with Ingester quick start, classification priority, customization example, and walker behavior notes

Design notes

The Ingester is a pure functional transform: Process returns []lore.Entry and the caller writes to Store + VectorStore. This keeps the ingester composable with any transactional or batching strategy.

Classification priority (first match wins):

1. YAML front matter kind: field
2. Path rules (filepath.Match globs, tested against both repo-relative path and basename)
3. Heading keywords in H1/H2/H3 text
4. Fallback: kind=research

Test plan

• go test -race ./pkg/lore/ingest/... passes
• go vet ./... clean
• gofmt -l ./pkg/lore/ingest/ produces no output
• PII grep zero matches