refactor: reduce complexity of copilot_args and configure::run

[github-actions]

Both src/engine.rs::copilot_args and src/configure.rs::run were flagged by clippy::cognitive_complexity at 27/25.

What was complex

copilot_args (src/engine.rs):

• A large if !use_allow_all_tools { ... } block (~85 lines) mixing three nested loops: extension tools, user MCP server scanning (with match config inside), and bash command collection.
• A for arg in engine.args() { for blocked in BLOCKED_ARG_PREFIXES { ... } } double loop at the bottom.

configure::run (src/configure.rs):

• A nested match pat { None => match try_azure_cli_token() { ... } } auth resolution block.
• An and_then(|url| { match parse_ado_remote { ... } }) closure inside the ADO context block.
• A large for m in matched { match update_pipeline_variable { Ok => ..., Err => ... } } update loop with counter tracking.

What changed

src/engine.rs

• collect_allowed_tools(front_matter, extensions, edit_enabled) -> Result<Vec<String>> — moves the entire restricted-tools collection block out of copilot_args. Handles extension tool names, user MCP server names, "write", and shell(<cmd>) entries.
• push_user_args(params, engine) -> Result<()> — moves the engine.args() validation + blocked-prefix check loop out of copilot_args.

src/configure.rs

• resolve_auth(pat) -> Result<AdoAuth> — extracts the PAT / Azure CLI / interactive-prompt fallback chain.
• resolve_ado_context(repo_path, org, project) -> Result<AdoContext> — extracts the git-remote parsing + CLI override logic.
• apply_token_updates(client, ado_ctx, auth, matched, token) -> Result<()> — extracts the per-definition update loop with success/failure counting and final error reporting.

Results

File	Function	Before	After
src/engine.rs	copilot_args	27	below 25 (no longer flagged)
src/configure.rs	run	27	below 25 (no longer flagged)

Only tests/compiler_tests.rs (complexity 29, a test helper with many assertion branches) remains — deferred as lower priority.

Verification

• All tests pass (cargo test)
• No new Clippy warnings introduced
• cargo clippy --all-targets --all-features -- -W clippy::cognitive_complexity no longer flags either file

Warning

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