feat(cli): add GlyphMode icon system, Theme extensions, and progress API

Phase 1 of UX skin overhaul: foundation layer that all subsequent
phases build upon.

Icons: 3-tier glyph system (Nerd Font / Unicode / ASCII) with
auto-detection from TERM_PROGRAM, LORE_ICONS env, or --icons flag.
16 semantic icon methods on Icons struct (success, warning, error,
issue states, MR states, note, search, user, sync, waiting).

Theme: 4 new semantic styles — muted (#6b7280), highlight (#fbbf24),
timing (#94a3b8), state_draft (#6b7280).

Progress: stage_spinner_v2 with icon prefix, nested_progress with
bounded bar/throughput/ETA, finish_stage for static completion lines,
format_elapsed for compact duration strings.

Utilities: format_relative_time_compact (3h, 2d, 1w, 3mo),
format_labels_bare (comma-separated without brackets).

CLI: --icons global flag, GLOBAL_FLAGS registry updated.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/cli/mod.rs

@@ -44,6 +44,10 @@ pub struct Cli {
     #[arg(long, global = true, value_parser = ["auto", "always", "never"], default_value = "auto", help = "Color output: auto (default), always, or never")]
     pub color: String,
 
+    /// Icon set: nerd (Nerd Fonts), unicode, or ascii
+    #[arg(long, global = true, value_parser = ["nerd", "unicode", "ascii"], help = "Icon set: nerd (Nerd Fonts), unicode, or ascii")]
+    pub icons: Option<String>,
+
     /// Suppress non-essential output
     #[arg(
         short = 'q',