feat(confluence): expose space enumeration as MCP tools

[mcp-atlassian-maintainer]

Finishes #1313 with the Confluence space enumeration tools rebased onto current main.

Summary

• Add the opt-in confluence_get_spaces tool with pagination and stable space metadata.
• Add the opt-in confluence_get_user_contributed_spaces tool.
• Register the confluence_spaces toolset without enabling it by default.
• Remove the unrelated workflow deletion from the original PR branch.

Testing

• uv run pytest tests/unit -xvs (3297 passed, 5 skipped)
• uv run pytest tests/e2e/cloud --cloud-e2e (89 passed, 15 skipped)
• uv run pytest tests/e2e --dc-e2e (99 passed, 105 skipped)

Contributor credit is preserved in the commit history.