fix(web-ui): restore padding inside flow chat cards

[bobleer]

Summary

• restore shared horizontal padding inside expanded FlowChat tool-card bodies
• add consistent four-sided padding to task prompts and projected subagent output
• preserve outer leading-edge alignment and full-bleed footer/list surfaces
• update the collapse spacing contract test for the revised layout rule

Type and Areas

Type:

Regression fix / UI/UX

Areas:

Web UI, FlowChat

Motivation / Impact

Subagent output and other expanded card content could render directly against the left border after the collapse-alignment change. This separates outer card alignment from internal content spacing, so cards stay aligned while their text keeps the shared FlowChat inset on every side.

Verification

• pnpm run type-check:web — passed
• pnpm --dir src/web-ui run test:run src/flow_chat/components/modern/FlowChatCollapseAlignment.test.ts — 4 tests passed
• git diff --check — passed

Reviewer Notes

Full-bleed result footers and Todo list surfaces consume the restored body inset with scoped negative margins, preserving their existing edge-to-edge treatment.

Checklist

• This PR is focused and does not include secrets, temporary prompts, generated scratch files, or unrelated artifacts.
• Relevant verification is recorded above, or skipped checks are explained.
• User-facing strings, docs, and locales are updated where applicable. No user-facing copy changed.