fix: improve MiniMax adaptor from PR #318 review (#319)

* feat: add MiniMax AI as LLM platform adaptor

Original implementation by octo-patch in PR #318.
This commit includes comprehensive improvements and documentation.

Code Improvements:
- Fix API key validation to properly check JWT format (eyJ prefix)
- Add specific exception handling for timeout and connection errors
- Remove unused variable in upload method

Dependencies:
- Add MiniMax to [all-llms] extra group in pyproject.toml

Tests:
- Remove duplicate setUp method in integration test class
- Add 4 new test methods:
  * test_package_excludes_backup_files
  * test_upload_success_mocked (with OpenAI mocking)
  * test_upload_network_error
  * test_upload_connection_error
  * test_validate_api_key_jwt_format
- Update test_validate_api_key_valid to use JWT format keys
- Fix test assertions for error message matching

Documentation:
- Create comprehensive MINIMAX_INTEGRATION.md guide (380+ lines)
- Update MULTI_LLM_SUPPORT.md with MiniMax platform entry
- Update 01-installation.md extras table
- Update INTEGRATIONS.md AI platforms table
- Update AGENTS.md adaptor import pattern example
- Fix README.md platform count from 4 to 5

All tests pass (33 passed, 3 skipped)
Lint checks pass

Co-authored-by: octo-patch <octo-patch@users.noreply.github.com>

* fix: improve MiniMax adaptor — typed exceptions, key validation, tests, docs

- Remove invalid "minimax" self-reference from all-llms dependency group
- Use typed OpenAI exceptions (APITimeoutError, APIConnectionError)
  instead of string-matching on generic Exception
- Replace incorrect JWT assumption in validate_api_key with length check
- Use DEFAULT_API_ENDPOINT constant instead of hardcoded URLs (3 sites)
- Add Path() cast for output_path before .is_dir() call
- Add sys.modules mock to test_enhance_missing_library
- Add mocked test_enhance_success with backup/content verification
- Update test assertions for new exception types and key validation
- Add MiniMax to __init__.py docstrings (module, get_adaptor, list_platforms)
- Add MiniMax sections to MULTI_LLM_SUPPORT.md (install, format, API key,
  workflow example, export-to-all)

Follows up on PR #318 by @octo-patch (feat: add MiniMax AI as LLM platform adaptor).

Co-Authored-By: Octopus <octo-patch@users.noreply.github.com>
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

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

docs/getting-started/01-installation.md

@@ -86,6 +86,7 @@ pip install skill-seekers[all-llms]
 - Claude AI support
 - Google Gemini support
 - OpenAI ChatGPT support
+- MiniMax AI support
 - All vector databases
 - MCP server
 - Cloud storage (S3, GCS, Azure)
@@ -98,6 +99,7 @@ Install only what you need:
 # Specific platform only
 pip install skill-seekers[gemini]      # Google Gemini
 pip install skill-seekers[openai]      # OpenAI
+pip install skill-seekers[minimax]     # MiniMax AI
 pip install skill-seekers[chroma]      # ChromaDB
 
 # Multiple extras
@@ -115,6 +117,7 @@ pip install skill-seekers[dev]
 |-------|-------------|-----------------|
 | `gemini` | Google Gemini support | `pip install skill-seekers[gemini]` |
 | `openai` | OpenAI ChatGPT support | `pip install skill-seekers[openai]` |
+| `minimax` | MiniMax AI support | `pip install skill-seekers[minimax]` |
 | `mcp` | MCP server | `pip install skill-seekers[mcp]` |
 | `chroma` | ChromaDB export | `pip install skill-seekers[chroma]` |
 | `weaviate` | Weaviate export | `pip install skill-seekers[weaviate]` |