v0.12.0

Atlassian connectors: Writer-gated write tools

Confluence, Jira, and Bitbucket were read-only, so Viewer/Writer did not change
their tool set. Added write tools gated behind <ID>_MODE (mirroring GitLab):
- Confluence: confluence_create_page, confluence_add_comment
- Jira: jira_create_issue, jira_add_comment
- Bitbucket: bitbucket_add_pr_comment
Viewer mode strips these via tool_router.remove_route; Writer exposes them.
Updated registry, site descriptions, and README. 24 E2E green; all three compile.