feat: add permission modes and CLI orchestration layer

Permission Modes:
- Add default/plan/auto_accept modes controlling tool access
- Plan mode restricts Task agent to read-only tools only
- Auto-accept mode bypasses approval prompts (with confirmation)

Approval Scaffolding:
- Add ApprovalRule/ApprovalRuleSet for granular tool control
- Pattern-based matching on tool name and arguments
- Default rules for common safe/dangerous patterns
- Prep for future bidirectional approval flow

CLI Refactor:
- Default to Task agent (main orchestrator)
- Add --mode flag and runtime mode switching
- Integrate prompt_toolkit for better UX:
  - Persistent command history (~/.webber_history)
  - Tab completion for commands and file paths
  - Auto-suggest from history
- Deprecate standalone 'explore' command

Other:
- Split CHANGELOG.md into per-package files
- Update AGENTS.md release procedure for both packages

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

webber-api/tests/test_task_agent.py

@@ -206,14 +206,14 @@ class TestTaskAgentProperties:
         # Create a fresh instance
         fresh_agent = TaskAgentImpl()
 
-        # _agent should be None before first access
-        assert fresh_agent._agent is None
+        # _agents dict should be empty before first access
+        assert len(fresh_agent._agents) == 0
 
-        # Access the agent property
+        # Access the agent property (creates default mode agent)
         _ = fresh_agent.agent
 
-        # Now _agent should be set
-        assert fresh_agent._agent is not None
+        # Now _agents should have one entry
+        assert len(fresh_agent._agents) == 1
 
 
 class TestAllAgentsRegistered: