feat(platform/bitbucket): remove deprecated issue tracking integration

[setchy]

Changes

Remove Bitbucket Cloud platform support for issues (create, list, update, close, etc).

Context

In anticipating of the imminent sunset of Bitbucket Cloud's native issue tracking - see https://community.atlassian.com/forums/Bitbucket-articles/Announcing-sunset-of-Bitbucket-Issues-and-Wikis/ba-p/3193882 😢

What’s changing?
Starting in April 2026, Issues and Wikis will no longer be available to turn on for repositories where these features are not currently used.
Existing Issues and Wikis will be fully sunset and removed from Bitbucket in mid-August, 2026.

Please select one of the following:

• This closes an existing Issue, Closes: #
• This doesn't close an Issue, but I accept the risk that this PR may be closed if maintainers disagree with its opening or implementation

AI assistance disclosure

Did you use AI tools to create any part of this pull request?

Please select one option and, if yes, briefly describe how AI was used (e.g., code, tests, docs) and which tool(s) you used.

• No — I did not use AI for this contribution.
• Yes — minimal assistance (e.g., IDE autocomplete, small code completions, grammar fixes).
• Yes — substantive assistance (AI-generated non‑trivial portions of code, tests, or documentation).
• Yes — other (please describe):

Documentation (please check one with an [x])

• I have updated the documentation, or
• No documentation update is required

How I've tested my work (please select one)

I have verified these changes via:

• Code inspection only, or
• Newly added/modified unit tests, or
• No unit tests, but ran on a real repository, or
• Both unit tests + ran on a real repository

The public repository:

[setchy]

I'll leave this in DRAFT state until Atlassian actually sunset the Issues/Wiki features