feat: complete Rust port of claude-statusline

Port the entire 2236-line bash statusline script to Rust.
Implements all 25 sections, 3-phase layout engine (render, priority
drop, flex/justify), file-based caching with flock, 9-level terminal
width detection, trend sparklines, and deep-merge JSON config.

Release binary: 864K with LTO. Render time: <1ms warm.

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

examples/custom-commands.json

@@ -0,0 +1,31 @@
+{
+  "version": 1,
+
+  "layout": [
+    ["model", "provider", "project", "vcs"],
+    ["context_bar", "cost", "duration", "ollama", "docker"]
+  ],
+
+  "custom": [
+    {
+      "id": "ollama",
+      "label": "ollama",
+      "command": "pgrep -x ollama >/dev/null && echo 'up' || echo 'down'",
+      "ttl": 30,
+      "priority": 3,
+      "color": {
+        "match": { "up": "green", "down": "dim" }
+      }
+    },
+    {
+      "id": "docker",
+      "label": "docker",
+      "command": "docker info >/dev/null 2>&1 && echo 'up' || echo 'down'",
+      "ttl": 60,
+      "priority": 3,
+      "color": {
+        "match": { "up": "green", "down": "dim" }
+      }
+    }
+  ]
+}

examples/dense.json

@@ -0,0 +1,10 @@
+{
+  "version": 1,
+  "layout": "dense",
+  "sections": {
+    "context_bar": {
+      "enabled": true, "priority": 1, "flex": true, "min_width": 10,
+      "bar_width": 8
+    }
+  }
+}

examples/user-config.json

@@ -0,0 +1,23 @@
+{
+  "comment": "User config — only include overrides. Merged with defaults.json at runtime.",
+  "layout": "verbose",
+  "global": {
+    "justify": "left",
+    "width_margin": 4
+  },
+  "sections": {
+    "version": {
+      "enabled": true
+    },
+    "hostname": {
+      "enabled": false
+    },
+    "cost": {
+      "thresholds": {
+        "warn": 2.00,
+        "danger": 5.00,
+        "critical": 10.00
+      }
+    }
+  }
+}

examples/verbose.json

@@ -0,0 +1,12 @@
+{
+  "version": 1,
+  "layout": "verbose",
+  "sections": {
+    "tokens_raw":      { "enabled": true, "priority": 3 },
+    "cache_efficiency": { "enabled": true, "priority": 3 },
+    "cost_velocity":   { "enabled": true, "priority": 3 },
+    "turns":           { "enabled": true, "priority": 3, "ttl": 2 },
+    "load":            { "enabled": true, "priority": 3, "ttl": 10 },
+    "version":         { "enabled": true, "priority": 3 }
+  }
+}