refactor: rename internal Fai* design system + fai_ helpers to chain

The Studio design system, widgets and helpers carried a Fai* / fai_
prefix (FaiSpace, FaiColors, FaiTheme, FaiLog, 17 fai_*.dart files, the
faiBinary* l10n keys). Studio is the Ch∆In product, so rename them to
Chain* / chain_ — carefully preserving English fail/failure/failed.
Also fix stale references: the 'fai' binary in l10n strings -> 'chain',
FAI_* env vars (FAI_BIN/DATA_DIR/MODULES_DIR/TODAY/BOOTSTRAP_TOKEN) ->
CHAIN_*, fai_platform -> fai_chain, fai_hub -> chain_hub. Vendor
security-hook tooling (FAI_BANNED_TERMS_FILE) + the .fai bundle ext left.
flutter analyze + test: clean (20 passed).

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

lib/widgets/fai_status_dot.dart

@@ -1,95 +0,0 @@
-// FaiStatusDot — small pulsing dot used as a "live" indicator.
-// Goes still when [pulsing] is false, breathes gently when true.
-
-import 'package:flutter/material.dart';
-
-import '../theme/tokens.dart';
-
-class FaiStatusDot extends StatefulWidget {
-  final Color color;
-
-  /// When true, the dot fades between full and 30% opacity.
-  /// When false, it stays at full opacity (steady-state).
-  final bool pulsing;
-
-  final double size;
-
-  const FaiStatusDot({
-    super.key,
-    required this.color,
-    this.pulsing = false,
-    this.size = 8,
-  });
-
-  @override
-  State<FaiStatusDot> createState() => _FaiStatusDotState();
-}
-
-class _FaiStatusDotState extends State<FaiStatusDot>
-    with SingleTickerProviderStateMixin {
-  late final AnimationController _ctrl;
-
-  @override
-  void initState() {
-    super.initState();
-    _ctrl = AnimationController(
-      vsync: this,
-      duration: const Duration(milliseconds: 1400),
-    );
-    if (widget.pulsing) _ctrl.repeat(reverse: true);
-  }
-
-  @override
-  void didUpdateWidget(covariant FaiStatusDot old) {
-    super.didUpdateWidget(old);
-    if (widget.pulsing && !_ctrl.isAnimating) {
-      _ctrl.repeat(reverse: true);
-    } else if (!widget.pulsing && _ctrl.isAnimating) {
-      _ctrl.stop();
-      _ctrl.value = 0;
-    }
-  }
-
-  @override
-  void dispose() {
-    _ctrl.dispose();
-    super.dispose();
-  }
-
-  @override
-  Widget build(BuildContext context) {
-    return AnimatedBuilder(
-      animation: _ctrl,
-      builder: (_, _) {
-        final t = widget.pulsing ? _ctrl.value : 0.0;
-        final alpha = 1.0 - (t * 0.6);
-        return Container(
-          width: widget.size,
-          height: widget.size,
-          decoration: BoxDecoration(
-            color: widget.color.withValues(alpha: alpha),
-            shape: BoxShape.circle,
-            boxShadow: widget.pulsing
-                ? [
-                    BoxShadow(
-                      color: widget.color.withValues(alpha: 0.4 * alpha),
-                      blurRadius: 6 * (1 + t),
-                      spreadRadius: 1 * t,
-                    ),
-                  ]
-                : const [],
-          ),
-        );
-      },
-    );
-  }
-}
-
-/// Convenience presets.
-class FaiStatusDots {
-  FaiStatusDots._();
-  static Widget live() =>
-      const FaiStatusDot(color: FaiColors.success, pulsing: true);
-  static Widget idle() => const FaiStatusDot(color: FaiColors.muted);
-  static Widget down() => const FaiStatusDot(color: FaiColors.danger);
-}