Add BitBucket support to init wizard

[acreeger]

Summary

Update the il init wizard prompt template to include BitBucket as a VCS provider option, add the bitbucket-pr merge mode, and document BitBucket credential configuration.

Context

The init wizard (init-prompt.txt) currently only lists local, github-pr, and github-draft-pr as merge mode options. There are no VCS provider configuration steps, no BitBucket credential documentation, and the JSON generation examples don't include versionControl config. New users setting up BitBucket have no guided path.

Epic item: #4 from #690

Files to Modify

• templates/prompts/init-prompt.txt (lines ~514-784)

Acceptance Criteria

• Init wizard presents bitbucket-pr as a merge mode option alongside local, github-pr, github-draft-pr
• Init wizard includes VCS provider selection step (GitHub vs BitBucket)
• BitBucket credential configuration is documented (username, API token in settings.local.json)
• JSON generation examples include versionControl config block for BitBucket
• Combined Jira+BitBucket configuration example is included
• Existing GitHub init flow is unaffected

Dependencies

None — can be worked in parallel with other child issues.

Scope Boundaries

• Only modifies the prompt template — does NOT change init command TypeScript code
• Does NOT add interactive BitBucket connection testing during init
• Does NOT modify SettingsManager schema (that was done in PR feat: add BitBucket integration for pull request management #609)