feat: SSML emotional TTS, agent avatars, AgentChat UX overhaul, virtual company enhancements

- SSML TTS with emotional styles (_build_ssml, mstts:express-as) and natural pauses
- Agent avatar support: DB migration, API, frontend emoji/URL rendering
- AgentChat UX: highlight.js code blocks, copy buttons, streaming cursor, char count,
  auto-title, keyboard shortcuts, message feedback (thumbs), undo delete, mobile responsive
- Virtual company: M2 control, tier-3/4 capabilities, per-dept session fix, deliverable
  validator, insight analyzer enhancements
- New services: agent_profiler, deliverable_validator, redis_task_registry
- Android: auth refactor, launcher icons, network security config, update manager
- Frontend: useSpeechQueue composable, Agents/AgentConfig/AgentTest enhancements
- Various backend fixes and expanded test coverage

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/alembic/versions/028_add_agent_avatar.py

@@ -0,0 +1,24 @@
+"""add agent avatar column
+
+Revision ID: 028_add_agent_avatar
+Revises: d684c9b30c1c
+Create Date: 2026-07-31
+"""
+
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision = '028_add_agent_avatar'
+down_revision = 'd684c9b30c1c'
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column('agents', sa.Column('avatar', sa.Text, nullable=True, comment='头像（emoji 或图片URL）'))
+
+
+def downgrade() -> None:
+    op.drop_column('agents', 'avatar')