✨ use the Linkit user picker to add group members

[zccz14]

What

The group manage panel adds members through the controlled LinkitUserPicker instead of a free-text username field:

• Controlled multi-select — LinkitUserPicker with multiple + value: string[] / onValueChange; each selected user ID posts straight to POST /api/conversations/{id}/members, dropping the username→profile lookup step.
• Picker search — matches username, UUID or private note, replacing the exact-username input; rows show the note name, username and full user ID.
• Locales — the form reuses group.membersPlaceholder ("Search username, UUID or note" / "搜索用户名、UUID 或备注"); the unused conversation.memberPlaceholder key is removed from en/zh.
• Unchanged — owner-only removal and its hint, the "add your Bot" list, and all server-side membership rules stay as delivered in ✨ let any group member add users while only the group owner removes members #163.

Release

• bump the crate to 0.1.101 (tag-driven release)

Complexity

• Net simplification: the add flow loses its two-step lookup mutation and free-text state; the picker owns search and selection. One locale key removed, none added.

Verification

• web: npm ci && npm run check — 51 tests pass, including the rewritten source-contract tests ("member adding uses the controlled multi user picker", "only the owner removes members"); typecheck, eslint, build, portal-layering all pass.
• packages/linkit-react-components: npm ci && npm run typecheck && npm test && npm run build && npm run pack:check — 56 tests pass.
• cargo fmt --check + cargo clippy --all-targets --all-features --locked -- -D warnings — clean (no Rust source changes in this PR).