Add script detection, env shebang parser, and opt-in content guessing

AGENTS.md

@@ -24,6 +24,7 @@ uv run rp <file>            # Rich-print a file
 uv run rp --help            # Show help
 uv run rp --version         # Show version
 echo '{"a":1}' | uv run rp  # Read from stdin
+cat patch.txt | uv run rp --guess-content  # Enable heuristic content guessing
 ```
 
 ### Testing
@@ -92,6 +93,7 @@ def detect_type(
     path: str | None = None,
     content: str | None = None,
     explicit_type: str | None = None,
+    guess_content: bool = False,
 ) -> str:
     ...
 ```
@@ -152,6 +154,11 @@ When adding new file types:
 2. Use Pygments lexer name as the value
 3. For special filenames (e.g., `Dockerfile`), add to `_FILENAME_MAP`
 
+Detection stays conservative by default: explicit type, filename map, extension map,
+shebang, and JSON detection all run before falling back to `text`. Heuristic
+Pygments content guessing is opt-in via `--guess-content` and should remain a
+late fallback.
+
 ### Rendering
 - `markdown` and `md` → use `rich.markdown.Markdown`
 - `json` → use `rich.json.JSON` with fallback to `Syntax`
@@ -190,9 +197,10 @@ rich-print/
 ## Dependencies
 
 - `rich>=13.0` — Terminal rendering (Markdown, JSON, Syntax)
+- `pygments>=2.13.0` — Lexer detection and syntax lexers
 - `typer>=0.12` — CLI framework
 
-Runtime dependencies. Dev dependencies: `ruff>=0.9`, `mypy>=1.14`, `pytest>=8.0`, `pytest-cov>=5.0`.
+Runtime dependencies. Dev dependencies: `ruff>=0.9`, `mypy>=1.14`, `pytest>=8.0`, `pytest-cov>=5.0`, `types-pygments>=2.19`.
 
 ## Git Workflow