fix: migration ModelName, reasoning_content, shell regex, loop boundary

1. migration.go: Set ModelName to userModel when provider matches so
   GetModelConfig(userModel) can find the entry. Previously the migration
   created entries with the provider name as ModelName (e.g. "moonshot")
   but lookup used the model name (e.g. "k2p5"), causing "model not found".

2. openai_compat/provider.go: Preserve reasoning_content in conversation
   history. Thinking models (e.g. Kimi K2, DeepSeek-R1) return
   reasoning_content which must be echoed back. Without it, APIs return
   400: "thinking is enabled but reasoning_content is missing".

3. shell.go: Fix deny pattern regex for format/mkfs/diskpart to use
   (?:^|\s) instead of \b to avoid matching --format flags.
   Fix path extraction regex to use submatch to avoid matching flags
   like -rf as paths.

4. loop.go: Adjust forceCompression mid-point to avoid splitting
   tool-call/result message pairs, which causes API errors.

pkg/providers/openai_compat/provider.go

@@ -289,10 +289,11 @@ func parseResponse(body []byte) (*LLMResponse, error) {
 // It mirrors protocoltypes.Message but omits SystemParts, which is an
 // internal field that would be unknown to third-party endpoints.
 type openaiMessage struct {
-	Role       string     `json:"role"`
-	Content    string     `json:"content"`
-	ToolCalls  []ToolCall `json:"tool_calls,omitempty"`
-	ToolCallID string     `json:"tool_call_id,omitempty"`
+	Role             string     `json:"role"`
+	Content          string     `json:"content"`
+	ReasoningContent string     `json:"reasoning_content,omitempty"`
+	ToolCalls        []ToolCall `json:"tool_calls,omitempty"`
+	ToolCallID       string     `json:"tool_call_id,omitempty"`
 }
 
 // stripSystemParts converts []Message to []openaiMessage, dropping the
@@ -302,10 +303,11 @@ func stripSystemParts(messages []Message) []openaiMessage {
 	out := make([]openaiMessage, len(messages))
 	for i, m := range messages {
 		out[i] = openaiMessage{
-			Role:       m.Role,
-			Content:    m.Content,
-			ToolCalls:  m.ToolCalls,
-			ToolCallID: m.ToolCallID,
+			Role:             m.Role,
+			Content:          m.Content,
+			ReasoningContent: m.ReasoningContent,
+			ToolCalls:        m.ToolCalls,
+			ToolCallID:       m.ToolCallID,
 		}
 	}
 	return out