fix(advisor): honor configured API URL

[wattswolf]

Summary

• Make actual advisor resolve its API base URL in this order: --api-url, non-empty ACTUAL_API_URL, configured api_url, production default.
• Preserve explicit overrides even if the local config file is malformed.

Fixes AK-415.

Proof

Acceptance behavior	Evidence
Configured staging/dev URL is honored	New regression test failed on main (production URL returned), then passed at 4b6a8596
Flag and environment overrides still win	Existing precedence test expanded; targeted suite passed 6/6
Default remains backward compatible	Missing configured URL still resolves to DEFAULT_API_URL
Regression test is meaningful	Reverting only the production change made the new test fail

Validation: cargo test --workspace --features integration (3,532 passed, 0 failed), cargo fmt --check, cargo clippy -- -D warnings, and cargo build --release.

Risk is limited to Advisor URL selection when no explicit override is supplied. Rollback is the single commit.