feat(bitbucket): add read-only branch restrictions fetch

[KatalKavya96]

Summary

• Adds magpie-bitbucket repo restrictions as a read-only Bitbucket repository branch restriction / branch permission context command.
• Fetches Bitbucket Cloud branch restrictions and Bitbucket Data Center branch permissions through read-only endpoints, including pagination.
• Normalizes branch restriction policy context into stable fields while keeping the adapter partial read-only and avoiding any repository permission or branch-rule mutation path.

Type of change

• Skill change (.claude/skills/<name>/) — eval fixtures updated below
• Tool / bridge contract (tools/<system>/*.md)
• Python package (tools/*/ with pyproject.toml)
• Groovy reference impl
• Cross-cutting (RFC, AGENTS.md, sandbox, privacy-LLM)
• Documentation (docs/, README.md, CONTRIBUTING.md)
• Project template (projects/_template/)
• CI / dev loop (prek, workflows, validators`)
• Other:

Test plan

• prek run --all-files passes
• For Python packages touched: PYTHONPATH=src uv run --group dev pytest tests/test_bitbucket.py -q
• For Python packages touched: PYTHONPATH=src uv run --group dev pytest tests/test_bitbucket.py -q -k "restrictions"
• For Python packages touched: uv run --group dev ruff check src tests --fix
• For Python packages touched: uv run --group dev ruff format src tests
• For Python packages touched: uv run --group dev mypy src tests
• For Groovy bridges touched: command-line invocation tested end-to-end
• For skill changes: eval suite passes for the affected skill
  (PYTHONPATH=tools/skill-evals/src python3 -m skill_evals.runner tools/skill-evals/evals/<skill>/)
• For skill behaviour changes: a new or updated eval fixture is included in this PR
  (a regression test for the bug fixed / the behaviour added — see CONTRIBUTING.md)
• Other:

RFC-AI-0004 compliance

• HITL — no mutation behaviour is added; the new command is read-only
• Sandbox — no new unrestricted host access; Bitbucket network reach remains declared in the adapter
• Vendor neutrality — extends the existing Bitbucket contract:change-request / Coverage: partial-read-only adapter without introducing a complete Bitbucket-specific source-control contract
• Conversational + correctable — agentic-override path remains documented for adopter-tunable behaviour
• Write-access discipline — this PR only reads branch restriction / branch permission context and does not create, update, delete, or bypass repository rules
• Privacy LLM — fetched branch restriction policy, users/groups/access keys where exposed, and raw Bitbucket payloads remain external data and are emitted as read-only bridge output for the caller to handle under existing privacy/approved-LLM rules

Linked issues

Refs #606

Notes for reviewers

This follows the recently merged Bitbucket read-only PR review-state and merge-check context commands and targets the next repository-context gap from the partial read-only roadmap.

The new command is:

magpie-bitbucket repo restrictions

It fetches repository-level branch restriction / branch permission context:

• Bitbucket Cloud: repository branch restrictions with pagination
• Bitbucket Data Center: repository branch permissions search with pagination

The normalized output includes restriction kind/type, branch matcher or pattern context, users, groups, access keys where exposed, permission-required metadata for Data Center, and raw backend payloads.

This is intentionally partial and read-only. Bitbucket Data Center branch permission search may require REPO_ADMIN, so the README documents that the command is permission-dependent. This PR does not mutate branch restrictions, repository permissions, access rules, pull requests, builds, issues, or repository content.

[KatalKavya96]

Hi @potiuk, I opened the next Bitbucket follow-up for #606.

This PR adds:

magpie-bitbucket repo restrictions

It fetches read-only repository branch restriction / branch permission context for Bitbucket Cloud and Data Center, including pagination, and normalizes restriction kind/type, branch pattern/matcher, users, groups, access keys where exposed, and raw payloads.

This remains partial read-only. Data Center may require REPO_ADMIN, and the command does not mutate branch rules, repository permissions, PRs, builds, issues, or repository content.

prek run --all-files and targeted Bitbucket pytest/ruff/mypy checks are passing.