Fix bugs, standardize error handling, add delete tools, and add tests

[adamweeks]

Critical bug fixes:

• Remove ~50 lines of dead/unreachable code after the except block in
  send_webex_message that was left from a half-finished refactor
• Fix the files parameter in send_webex_message — the SDK requires a list
  but a bare string was being passed, silently breaking file attachments
• Fix timestamp field in create_error_response/create_success_response;
  REQUEST_TIMESTAMP env var is never set so the field was always empty string;
  now uses datetime.now(timezone.utc).isoformat()

Architecture:

• Remove double load_dotenv() call (was in both main.py and tools/common.py)
• Remove redundant WEBEX_ACCESS_TOKEN check in main.py (tools/common.py
  already validates and raises on import)

Error handling — all tools now use structured responses:

• Standardize rooms.py, memberships.py, people.py, and the remaining
  message functions to use create_error_response / create_success_response
  with WebexErrorCodes (previously returned bare dicts with no error codes)
• Extract _map_exception_to_error() and _*_to_dict() helpers in each module
  to eliminate repetitive per-field exception handling

New tools (missing CRUD operations):

• delete_webex_room / delete_webex_space
• delete_webex_membership
• delete_webex_message

Code quality:

• Consolidate duplicate mention-building logic in send_webex_message_with_mentions
  to use the existing create_message_with_mentions helper
• Rename id parameter to person_id in list_webex_people (shadowed built-in)
• Update _build_message_params shared helper used by both message send functions

Config / metadata fixes:

• Fix log level validation: accept "WARNING" not "WARN" (standard Python logging)
• Fix pyproject.toml: rename dotenv -> python-dotenv, bump version to 1.0.0,
  add real description
• Fix resources_count in version resource (was 8, now 10)
• Update tools_count to 31 (added 3 delete tools + 2 delete aliases)

Tests (new):

• tests/test_messages.py: 38 unit tests covering mention formatters,
  create_message_with_mentions, send_webex_message validation, files wrapping,
  list/delete, response builders, and WebexConfig; mocks webexpythonsdk at
  sys.modules level so no real credentials are needed

Documentation:

• Add CLAUDE.md with full developer guide: layout, conventions, error code
  ranges, response shape, how to add a new tool, env var reference

https://claude.ai/code/session_01KTZNsi11DycdLENcbUUbgU