feat(tools/bitbucket): Bitbucket forge + tracker bridge (Atlassian)

[potiuk]

Add tools/bitbucket/ as a forge + tracker bridge for Bitbucket (Atlassian Cloud and self-hosted Data Center), analogous to tools/github/ and the tools/gitlab/ bridge (#305). Bitbucket is a major Git forge with no coverage today, and it has deep Jira integration — pairing naturally with the existing tools/jira/ tracker bridge.

Capabilities to provide (mirror the GitHub bridge):

• Issue read/write (Bitbucket issues and linked Jira, via tools/jira/)
• Pull-request read/write: view/list, create/edit/merge, comment, review/approve
• Repo metadata, branch permissions
• Pipelines read for CI status checks
• Bitbucket Cloud REST API + Data Center REST API (note: the two API flavours differ — abstract behind one bridge)

Why: Bitbucket is the default forge across the Atlassian enterprise ecosystem and a large share of corporate OSS. It historically hosted Mercurial too (dropped in 2020), which is part of why Hg projects scattered — so a Bitbucket bridge plus the Mercurial bridge together recover that displaced population. With Jira already bridged, Bitbucket closes the loop on the full Atlassian adopter stack.

Reference:

• Bitbucket Cloud REST API: https://developer.atlassian.com/cloud/bitbucket/rest/
• Bitbucket Data Center REST API: https://developer.atlassian.com/server/bitbucket/rest/
• Existing forge bridges to mirror: tools/github/, tools/gitlab/ (feat(tools/gitlab): add tracker + forge bridge for GitLab-hosted projects #305); pairs with tools/jira/