Fix New Agent drawer clipping and scrollbar overlap

[pratikbuilds]

Closes #690

Summary

• Add a scoped New Agent drawer class so overflow rules do not affect other dialogs.
• Reserve balanced inline space for focus rings and the scrollbar gutter.
• Constrain drawer children and form controls to the available width.
• Add regression coverage that verifies the overflow rules are scoped to this panel.

Evidence

The issue contains the original defect screenshot and the fixed-state screenshot.

Validation

• Focused CreateAgentPanel tests: 12 passed
• Typecheck: passed before the upstream rebase
• Production build: passed
• Live browser verification: passed at desktop and shorter viewport heights
• Full repository check is currently blocked by unrelated upstream main errors in templates/connectors.ts for the newly landed Codex/XAI provider constants; details are recorded in the task handoff.

[TheGreatAxios]

Recommendation: strengthen regression coverage; shared drawer styling is a recommendation, not a demonstrated blocker.

Updated after a factual second pass. The change is feature-scoped, but this source review does not establish rendered overflow behavior or reproduce the issue in sibling drawers.

Should fix

1. The test pins class wiring, not the overflow rules or behavior. apps/web/test/create-agent-panel.test.tsx:166 checks the DialogContent class. Deleting the new CSS leaves that assertion green, so it does not establish the described regression coverage for scoped overflow rules. A source assertion can check selector scoping; a rendered regression test is needed to prove the overflow behavior.

Recommendations and nits

• Consider sharing demonstrated drawer-wide invariants. The shared dialog-craft section at apps/web/src/app.css:191 is a plausible home for right-drawer rules. However, using the same primitive does not prove that the plugin and invite drawers reproduce this bug. Keep feature-specific rules local unless that broader behavior is established.
• The insertion separates the existing quiet-field comment from its rule at apps/web/src/app.css:2990; keep the comment with the rule it describes.
• Review whether the standalone root and child min-width rules are necessary in the current layout. My earlier claim that three of four blocks were no-ops was inaccurate: the body block at apps/web/src/app.css:2997 and form-control block at apps/web/src/app.css:3010 contain substantive rules.

Correction to the original review: sibling overflow, successful rendered behavior, and future padding double-compensation were not demonstrated. They should not have been stated as established defects.