feat(F-09): rich parsing — formula + figure extraction

- codex/parsing/mathpix.py: pix2tex (local, CPU) primary + MathPix API
  optional; bbox heuristic h>15px, math-char-count>5; singleton model cache
- codex/parsing/figures.py: pymupdf embedded-image extraction → PNG;
  caption detection via proximity + "Figure/Fig./Abbildung" prefix
- codex/models.py: FormulaChunk + FigureChunk dataclasses (R-10/R-11)
- codex/ingest.py: --rich flag wires formula+figure extraction post-ingest
- codex/cli.py: search_app sub-typer (paper + formula subcommands),
  --rich flag on ingest; wiki_app from F-12 preserved intact
- codex/config.py: mathpix_app_id/key, pix2tex_fallback, figures_dir
- infra/schema.sql: formulas + figures tables with HNSW pgvector indexes
- pyproject.toml: pymupdf>=1.24, pix2tex>=0.1.4
- tests/parsing/test_mathpix.py + test_figures.py: 31 tests (mock pix2tex
  + MathPix HTTP, real pymupdf on synthetic PDF)

Gate: 158 passed, ruff clean, mypy clean (20 files)
Requirements: R-10 R-11 R-12 R-13 R-14 → done

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

infra/schema.sql

@@ -88,3 +88,37 @@ CREATE INDEX code_links_paper_idx  ON code_links (paper_id);
 -- GROUP  BY cited_id
 -- ORDER  BY pull DESC
 -- LIMIT  20;
+
+-- ---------------------------------------------------------------------
+-- F-09 Rich Parsing: formulas + figures
+-- ---------------------------------------------------------------------
+CREATE TABLE IF NOT EXISTS formulas (
+    id          BIGSERIAL PRIMARY KEY,
+    paper_id    TEXT REFERENCES papers(id) ON DELETE CASCADE,
+    page        INT,
+    raw_latex   TEXT NOT NULL,
+    context     TEXT,
+    eq_label    TEXT,
+    embedding   vector(1024)
+);
+
+CREATE INDEX IF NOT EXISTS formulas_emb_idx
+    ON formulas USING hnsw (embedding vector_cosine_ops);
+CREATE INDEX IF NOT EXISTS formulas_paper_idx ON formulas (paper_id);
+CREATE INDEX IF NOT EXISTS formulas_fts_idx
+    ON formulas USING gin (
+        to_tsvector('english', raw_latex || ' ' || coalesce(context, ''))
+    );
+
+CREATE TABLE IF NOT EXISTS figures (
+    id          BIGSERIAL PRIMARY KEY,
+    paper_id    TEXT REFERENCES papers(id) ON DELETE CASCADE,
+    page        INT,
+    caption     TEXT,
+    image_path  TEXT,
+    embedding   vector(1024)
+);
+
+CREATE INDEX IF NOT EXISTS figures_emb_idx
+    ON figures USING hnsw (embedding vector_cosine_ops);
+CREATE INDEX IF NOT EXISTS figures_paper_idx ON figures (paper_id);