Fix studio status to show full markdown-formatted summary

Changes:
- Fix JSON path for session logs: now reads from context_window.conversation_history
  (with fallback to messages for backwards compatibility)
- Remove 500-character truncation to show full summary
- Add termimad dependency for terminal markdown rendering
- Display summary with proper markdown formatting (headers, bold, code, lists)

The extract_session_summary() function was looking for messages at the wrong
JSON path. Session logs store conversation history at context_window.conversation_history,
not at the top-level messages key.

Cargo.lock

@@ -1370,7 +1370,7 @@ dependencies = [
  "sha2",
  "syntect",
  "tempfile",
- "termimad",
+ "termimad 0.34.0",
  "tokio",
  "tokio-util",
  "tracing",
@@ -3446,6 +3446,7 @@ dependencies = [
  "clap",
  "serde",
  "serde_json",
+ "termimad 0.31.3",
  "tokio",
  "uuid",
 ]
@@ -3539,6 +3540,22 @@ dependencies = [
  "windows-sys 0.61.2",
 ]
 
+[[package]]
+name = "termimad"
+version = "0.31.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7301d9c2c4939c97f25376b70d3c13311f8fefdee44092fc361d2a98adc2cbb6"
+dependencies = [
+ "coolor",
+ "crokey",
+ "crossbeam",
+ "lazy-regex",
+ "minimad",
+ "serde",
+ "thiserror 2.0.17",
+ "unicode-width 0.1.14",
+]
+
 [[package]]
 name = "termimad"
 version = "0.34.0"