refactor

[hit9]

• Add plan mode
• update plan mode prompt
• Add plan mode timeouts
• Reject chat actions in plan mode
• Add LSP tools implementation plan
• Compact observed tool call context
• Revert "Add LSP tools implementation plan"
• Keep status bar visible during prompt
• Add completion pressure gate for settled tasks
• Move runtime data to global session storage
• Add changelog for 0.3.17
• Improve model reasoning selector UI
• Add provider model selector
• Add provider selector command
• Disallow reading provider secrets via set command
• Bump version to 0.3.18
• Refine observe evidence context management
• Tighten ACT and observe prompt guidance
• Skip active sessions when cleaning logs
• Guide ACT action frontier selection
• Refine evidence display and provider options
• Clear task-local evidence on new goals
• Require observe coverage for tool results
• Clarify Search glob usage