chore(release): 0.0.3

Squash-merge lib-standardisation: adopt repo standards across packaging,
tooling, docs, and CI.

- standardize pyproject.toml (canonical packaging, lint config, extras, GSDFC pydoclint)
- add py.typed marker, modernize type hints and Google-style docstrings
- nest generated docs under docs/lib and docs/mcp; add hand-written wiki
- adopt standard Type A PyPI CI pipeline (tag==version guard + quality gate)
- promote generated CHANGELOG.md; bump version to 0.0.3

docs/wiki/03_extending.md

@@ -0,0 +1,104 @@
+# 🧩 Extending OmniRead
+
+OmniRead is meant to be extended by subclassing. All public extension points
+are generic over their result type, so your parser returns exactly the shape
+you need.
+
+---
+
+## 🧬 Custom parsers
+
+Subclass `BaseParser[T]` (or a format parser) and implement `parse()`:
+
+```python
+from pydantic import BaseModel
+from omniread import HTMLParser
+
+class Page(BaseModel):
+    title: str
+    content: str | None
+
+class PageParser(HTMLParser[Page]):
+    def parse(self) -> Page:
+        soup = self._soup
+        div = soup.find("div", id="content")
+        return Page(
+            title=soup.title.string,
+            content=div.get_text() if div else None,
+        )
+```
+
+The parsed page is validated by Pydantic on construction — no manual
+assertions required.
+
+---
+
+## 🧬 Custom PDF parsers
+
+PDF binary layout is format-specific, so parsers return your own model:
+
+```python
+from typing import Literal
+from pydantic import BaseModel
+from omniread import PDFParser
+
+class ParsedPDF(BaseModel):
+    size_bytes: int
+    magic: Literal[b"%PDF"]
+
+class SimplePDFParser(PDFParser[ParsedPDF]):
+    def parse(self) -> ParsedPDF:
+        if not self.content.raw.startswith(b"%PDF"):
+            raise ValueError("Not a valid PDF")
+        return ParsedPDF(size_bytes=len(self.content.raw), magic=b"%PDF")
+```
+
+---
+
+## 🧬 Custom clients
+
+Clients supply raw bytes to a scraper. For PDFs, subclass
+`BasePDFClient` (or `FileSystemPDFClient`) and implement
+`fetch(source) -> bytes`:
+
+```python
+from omniread.pdf.client import BasePDFClient
+
+class MockPDFClient(BasePDFClient):
+    def fetch(self, source):
+        return b"%PDF ..."  # bytes for the logical identifier
+```
+
+The same pattern applies to `BaseCsvClient` and `BaseXlsxClient`.
+
+---
+
+## 🚀 Custom scrapers
+
+Festch something that a built-in scraper does not cover by extending
+`BaseScraper`:
+
+```python
+from omniread import BaseScraper, Content, ContentType
+
+class StorageScraper(BaseScraper):
+    def fetch(self, source, *, metadata=None):
+        raw = my_object_storage.download(source)      # your I/O
+        return Content(raw=raw, source=source, content_type=ContentType.JSON)
+```
+
+---
+
+## ✅ Extension checklist
+
+1. Keep **scraper** and **parser** separate — never mix I/O into `parse()`.
+2. Return `Content` from any scraper/client so downstream stays uniform.
+3. Return a *typed* result from your parser (Pydantic model, dataclass, str).
+4. Test your custom layers with a mock client, not a live network.
+
+---
+
+## 📚 Read Next
+
+- [How to Use](02_how_to_use.md) — built-in example flows.
+- [Development](04_development.md) — running tests and docs.