refactor: reduce complexity of execute_impl in create_branch.rs

[github-actions]

What was complex

CreateBranchResult::execute_impl in src/safe_outputs/create_branch.rs was flagged by clippy::too_many_lines at 160/100 lines. It mixed four distinct concerns inline:

1. Policy validation (branch-pattern regex, allowed-repositories, allowed-source-branches)
2. Repository/branch resolution (source commit vs. source branch → SHA)
3. Request construction (ref name normalization, API URL)
4. HTTP submission and response interpretation (including per-ref success/error handling embedded in an otherwise-2xx response)

What changed

Extracted 6 single-purpose helper functions, each handling one concern:

• check_branch_pattern — validates the branch name against the configured branch-pattern regex
• check_allowed_repository — validates the repository alias against allowed-repositories
• check_allowed_source_branch — validates the source branch against allowed-source-branches
• resolve_source_sha — resolves source_commit (if given) or looks up source_branch via the refs API
• qualified_ref_name — normalizes a branch name to its refs/heads/... form
• submit_branch_creation — POSTs the ref-creation request and interprets the HTTP/per-ref response

execute_impl itself shrank to a ~45-line orchestrator that calls these helpers in sequence. No public API signatures or observable behavior changed.

Before/after complexity

	Lines
Before	160 (clippy::too_many_lines threshold: 100)
After	not flagged by clippy::too_many_lines

Validation

• cargo test --bin ado-aw create_branch — 17/17 passed
• cargo test --bin ado-aw — 3408 passed, 0 failed, 1 ignored (full suite, no regressions)
• cargo clippy --all-targets --all-features — no new warnings (only pre-existing, unrelated async_trait double_must_use warnings tracked separately in open PR fix(clippy): bump async-trait to 0.1.92 to clear double_must_use lint #2296)
• Re-ran the too_many_lines lint scoped to this file: execute_impl no longer appears in the violations list

Warning

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Generated by Cyclomatic Complexity Reducer · auto · 93.6 AIC · ⌖ 7.59 AIC · ⊞ 11.1K · ◷

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