Address 8 issues found in spec audit (post PR #2):
1. §refs label: distinguish design vs report sections in p3-1 / p3-2 / p4-2 /
p9-1 / p9-5 contract_sections (e.g., "report §11.2 Ollama" not "§11.2").
2. mock feature gate: gate MockEmbedder (p3-1) and MockLanguageModel (p4-1)
behind `mock` cargo feature, default OFF; add CI symbol-scan as DoD item.
3. Warning type unification: p1-2 frontmatter now emits
`kb_parse_types::Warning` (matches p1-3 / p1-4); drops crate-internal type.
4. p4-3 streaming thread: explicitly single-threaded inside RagPipeline::ask;
collection + sink.send share the calling thread, no race. UI concurrency
is callers responsibility (TUI worker thread pattern in p9-3).
5. p6-2 tesseract version: noted that `tesseract` 0.13 has no stable Rust
`version()` accessor; use TessVersion FFI or shell-out + cache approach.
6. p9-* App struct extensions: introduce `kb_tui::{Library,Search,Ask,Inspect}State`
slots in p9-1 forward-decl form; p9-2/3/4 fill bodies in their own crate
without editing `App`. Parallel-safety contract added.
7. p3-3 cosine score: shift `(sim+1)/2` instead of clamp; preserve ranking
signal between unrelated and opposite vectors. Clamp reserved for NaN.
8. fixtures/ root: p0-1 DoD now creates all fixture subdirs with .gitkeep so
downstream tasks have a stable target path.
