Fix Phabricator URL action references

[ShreyanshGoyal]

Summary

• expose the canonical url field in successful Phabricator submission results
• retain revision_url for compatibility with existing consumers
• cover the documented action-reference contract in the handler test

Rationale

The phabricator.submit_patch action tells agents to reference a submitted revision with {{actions.<ref>.url}}. The apply handler returned only revision_url, so the placeholder resolver could not find url and left the literal reference in Bugzilla comments. Returning the documented alias makes those references resolvable without breaking consumers of revision_url.

Fixes #6330.

Test plan

• Confirmed the updated handler assertion fails before the source change
• python -m pytest libs/hackbot-runtime/tests/test_phabricator_handler.py libs/hackbot-runtime/tests/test_phabricator_actions.py -q (18 passed)
• python -m ruff check and python -m ruff format --check on the changed Python files
• python -m compileall -q libs/hackbot-runtime/hackbot_runtime/actions/handlers/phabricator_handler.py