feat: PDF support + Split View (P1 roadmap items)

#74 — Support PDF complet:
- backend/pdf_reader.py — pymupdf/pypdf text extraction
- .pdf added to SUPPORTED_EXTENSIONS in indexer.py
- PDF-aware file view API endpoint (metadata, text preview)
- Streaming endpoint /api/file/{vault}/pdf/stream
- Frontend PDF viewer with iframe, toolbar, download
- CSS for PDF viewer container

#75 — Split View (PaneManager):
- New module frontend/js/pane-manager.js — ES module
- 1-4 pane CSS grid with resize handles
- Split right/down via keyboard (Ctrl+Alt+\) or PaneManager API
- Persistence in localStorage (obsigate-panes)
- Collapse to single pane, per-pane active state

285 tests passent

backend/pdf_reader.py

@@ -0,0 +1,92 @@
+"""PDF text extraction for ObsiGate — pypdf backend, pymupdf optional fallback."""
+from __future__ import annotations
+
+import logging
+from pathlib import Path
+
+logger = logging.getLogger(__name__)
+
+PDF_READER: str = "pypdf"
+try:
+    import fitz  # pymupdf
+    PDF_READER = "pymupdf"
+    logger.info("PDF reader: pymupdf (high performance)")
+except ImportError:
+    try:
+        from pypdf import PdfReader  # type: ignore
+        logger.info("PDF reader: pypdf (pure Python)")
+    except ImportError:
+        PdfReader = None  # type: ignore
+        logger.warning("No PDF reader available — install pypdf or pymupdf")
+
+
+def extract_pdf_text(file_path: Path, max_chars: int = 100000) -> str:
+    """Extract text from a PDF file. Returns empty string on failure."""
+    if PdfReader is None and PDF_READER == "pypdf":
+        return ""
+    try:
+        if PDF_READER == "pymupdf":
+            return _extract_pymupdf(file_path, max_chars)
+        else:
+            return _extract_pypdf(file_path, max_chars)
+    except Exception as e:
+        logger.warning("Failed to extract PDF text from %s: %s", file_path, e)
+        return ""
+
+
+def extract_pdf_metadata(file_path: Path) -> dict:
+    """Extract metadata from a PDF file."""
+    info = {"pages": 0, "title": "", "author": ""}
+    try:
+        if PDF_READER == "pymupdf":
+            doc = fitz.open(str(file_path))
+            info["pages"] = doc.page_count
+            meta = doc.metadata or {}
+            info["title"] = meta.get("title", "")
+            info["author"] = meta.get("author", "")
+            doc.close()
+        else:
+            reader = PdfReader(str(file_path))
+            info["pages"] = len(reader.pages)
+            meta = reader.metadata or {}
+            if meta:
+                info["title"] = str(meta.get("/Title", ""))
+                info["author"] = str(meta.get("/Author", ""))
+    except Exception as e:
+        logger.warning("Failed to extract PDF metadata from %s: %s", file_path, e)
+    return info
+
+
+def _extract_pymupdf(file_path: Path, max_chars: int) -> str:
+    doc = fitz.open(str(file_path))
+    parts = []
+    total = 0
+    for page in doc:
+        text = page.get_text()
+        if text:
+            if total + len(text) > max_chars:
+                remaining = max_chars - total
+                if remaining > 0:
+                    parts.append(text[:remaining])
+                break
+            parts.append(text)
+            total += len(text)
+    doc.close()
+    return "\f".join(parts)
+
+
+def _extract_pypdf(file_path: Path, max_chars: int) -> str:
+    reader = PdfReader(str(file_path))
+    parts = []
+    total = 0
+    for page in reader.pages:
+        text = page.extract_text() or ""
+        if text:
+            if total + len(text) > max_chars:
+                remaining = max_chars - total
+                if remaining > 0:
+                    parts.append(text[:remaining])
+                break
+            parts.append(text)
+            total += len(text)
+    return "\f".join(parts)