Document intentional error suppressions with comments (gt-zn9m)

All 156 instances of _ = error suppression in non-test code now have
explanatory comments documenting why the error is intentionally ignored.

Categories of intentional suppressions:
- non-fatal: session works without these - tmux environment setup
- non-fatal: theming failure does not affect operation - visual styling
- best-effort cleanup - defer cleanup on failure paths
- best-effort notification - mail/notifications that should not block
- best-effort interrupt - graceful shutdown attempts
- crypto/rand.Read only fails on broken system - random ID generation
- output errors non-actionable - fmt.Fprint to io.Writer

This addresses the silent failure and debugging concerns raised in the
issue by making the intentionality explicit in the code.

Generated with Claude Code https://claude.com/claude-code

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

internal/cmd/down.go

@@ -141,7 +141,7 @@ func stopSession(t *tmux.Tmux, sessionName string) error {
 		return nil // Already stopped
 	}
 
-	// Try graceful shutdown first (Ctrl-C)
+	// Try graceful shutdown first (Ctrl-C, best-effort interrupt)
 	if !downForce {
 		_ = t.SendKeysRaw(sessionName, "C-c")
 		time.Sleep(100 * time.Millisecond)