Code quality improvements and test fixes (#592)

## Summary
Comprehensive post-v3.0.0 modernization: new features, bug fixes,
dependency cleanup, docs, and test coverage.

**New features:**
- **HTTP method filtering** — `@api.route("/data", methods=["GET"])`
- **Lifespan context manager** — modern async startup/shutdown
- **`api.exception_handler()`** — custom error handling per exception
type
- **`api.graphql()`** — one-liner GraphQL setup
- **`resp.file()`** — serve files from disk with auto content-type
- **before_request short-circuit** — set status code to skip route
handler
- **`req.path_params`** / **`req.client`** / **`req.is_json`** — new
request properties
- **`uuid`** and **`path`** route convertors
- **PEP 561 `py.typed`** marker

**Bug fixes:**
- Fix multipart parser losing headers
- Fix `url_for()` with typed params (`{id:int}`)
- Fix `resp.body` encoding crash on bytes content
- Fix Python 3.9 type syntax (`from __future__ import annotations`)
- Fix broken session test and no-op file upload test
- Fix helloworld example 404 on root path

**Dependencies:**
- Flattened — `pip install responder` gets everything
- Core: just starlette + uvicorn (down from 10 deps)

**Docs & README:**
- All new features documented in tour
- Modernized README features list
- Deployment guide: Docker, cloud, uvicorn
- Removed Pipenv, extras, stale references throughout

**Tests & quality:**
- 117 tests (up from 92), 91% coverage, 0 warnings
- CaseInsensitiveDict, GraphQL edge cases, staticfiles tests
- Ruff clean, all `tmpdir` → `tmp_path`

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.github/workflows/test.yaml

@@ -25,7 +25,6 @@ jobs:
           "3.11",
           "3.12",
           "3.13",
-          "pypy3.10",
         ]
     env:
       UV_SYSTEM_PYTHON: true
@@ -50,34 +49,6 @@ jobs:
         cache-dependency-glob: |
           pyproject.toml
 
-    - name: Install and validate package
-      run: |
-        uv pip install '.[full,develop,test]'
-        poe check
-
-
-  test-minimal:
-    name: "Minimal"
-    runs-on: ubuntu-latest
-    env:
-      UV_SYSTEM_PYTHON: true
-
-    steps:
-    - uses: actions/checkout@v4
-
-    - name: Set up Python
-      uses: actions/setup-python@v5
-      with:
-        python-version: "3.13"
-
-    - name: Set up uv
-      uses: astral-sh/setup-uv@v5
-      with:
-        version: "latest"
-        enable-cache: true
-        cache-dependency-glob: |
-          pyproject.toml
-
     - name: Install and validate package
       run: |
         uv pip install '.[develop,test]'