feat: v1.0.0 release readiness

[CodeKeanu]

Summary

This PR addresses the v1.0 readiness checklist from issue #29:

• Updated version to 1.0.0 in pyproject.toml and server.py
• Changed development status from "Alpha" to "Production/Stable"
• Added missing unit tests for 3 endpoint modules (13 tools now covered)
• Removed duplicate _resolve_steam_id methods, consolidated to base class
• Updated CHANGELOG.md with v1.0.0 release notes

Changes

Version Updates

• pyproject.toml: version 0.8.0 → 1.0.0
• pyproject.toml: status 3 - Alpha → 5 - Production/Stable
• server.py: server_version 0.1.0 → 1.0.0

New Test Coverage

• tests/test_steam_user.py - 6 tools (get_my_steam_id, get_player_summary, get_player_summaries, resolve_vanity_url, get_friend_list, get_player_bans)
• tests/test_user_stats.py - 6 tools (get_player_achievements, get_game_schema, get_global_achievement_percentages, get_user_stats_for_game, get_current_players, get_global_stats_for_game)
• tests/test_steam_news.py - 1 tool (get_news_for_app)

Code Consolidation

• Removed duplicate _resolve_steam_id from steam_user.py, user_stats.py, player_service.py, steam_trading.py
• All endpoints now use the base class implementation in BaseEndpoint._resolve_steam_id()
• Cleaned up unused imports

Documentation

• Added v1.0.0 entry to CHANGELOG.md

Testing

• All 319 existing tests pass
• New tests for steam_user, user_stats, steam_news endpoints pass
• Ruff linting passes for new test files

Checklist from Issue

• pyproject.toml line 7: Update version from 0.8.0 to 1.0.0
• server.py line 128: Update server_version from "0.1.0" to "1.0.0"
• Add tests/test_steam_user.py (6 tools)
• Add tests/test_user_stats.py (6 tools)
• Add tests/test_steam_news.py (1 tool)
• steam_user.py - remove duplicate, use self._resolve_steam_id() from base
• user_stats.py - remove duplicate
• player_service.py - remove duplicate
• Update development status to 5 - Production/Stable
• Update CHANGELOG.md with release notes

Closes #29

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