fix: replace silent exception swallowing with debug logging across tools

Add logger.debug() calls to 27 bare 'except: pass' blocks across 7 core
files, giving visibility into errors that were previously silently
swallowed. This makes it much easier to diagnose user-reported issues
from debug logs.

Files changed:
- tools/terminal_tool.py: 5 catches (stat, termios, fd close, cleanup)
- tools/delegate_tool.py: 7 catches + added logger (spinner, callbacks)
- tools/browser_tool.py: 5 catches (screenshot/recording cleanup, daemon kill)
- tools/code_execution_tool.py: 2 remaining catches (socket, server close)
- gateway/session.py: 2 catches (platform enum parse, temp file cleanup)
- agent/display.py: 2 catches + added logger (JSON parse in failure detect)
- agent/prompt_builder.py: 1 catch (skill description read)

Deliberately kept bare pass for:
- ImportError checks for optional dependencies (terminal_tool.py)
- SystemExit/KeyboardInterrupt handlers
- Spinner _write catch (would spam on every frame when stdout closed)
- process_registry PID-alive check (canonical os.kill(pid,0) pattern)

Extends the pattern from PR #686 (@aydnOktay).

gateway/session.py

@@ -272,8 +272,8 @@ class SessionEntry:
         if data.get("platform"):
             try:
                 platform = Platform(data["platform"])
-            except ValueError:
-                pass
+            except ValueError as e:
+                logger.debug("Unknown platform value %r: %s", data["platform"], e)
         
         return cls(
             session_key=data["session_key"],
@@ -370,8 +370,8 @@ class SessionStore:
         except BaseException:
             try:
                 os.unlink(tmp_path)
-            except OSError:
-                pass
+            except OSError as e:
+                logger.debug("Could not remove temp file %s: %s", tmp_path, e)
             raise
     
     def _generate_session_key(self, source: SessionSource) -> str: