feat(tools): add WeatherTool with wttr.in integration (#4104)

Implements the Weather integration as a native Rust Tool trait
implementation, consistent with the existing first-party tool
architecture (no WASM/plugin layer required).

- Add src/tools/weather_tool.rs with full WeatherTool impl
  - Fetches from wttr.in ?format=j1 (no API key, global coverage)
  - Supports city names (any language/script), IATA airport codes,
    GPS coordinates, postal/zip codes, domain-based geolocation
  - Metric (°C, km/h, mm) and imperial (°F, mph, in) units
  - Current conditions + 0-3 day forecast with hourly breakdown
  - Graceful error messages for unknown/invalid locations
  - Respects runtime proxy config via apply_runtime_proxy_to_builder
  - 36 unit tests: schema, URL building, param validation, formatting
- Register WeatherTool unconditionally in all_tools_with_runtime
  (no API key needed, no config gate — same pattern as CalculatorTool)
- Flip integrations registry Weather entry from ComingSoon to Available

Closes #<issue>

src/integrations/mod.rs

@@ -155,6 +155,13 @@ fn show_integration_info(config: &Config, name: &str) -> Result<()> {
             println!("    Schedule tasks in ~/.zeroclaw/workspace/cron/");
             println!("    Run: zeroclaw cron list");
         }
+        "Weather" => {
+            println!("  Built-in:");
+            println!("    Fetches live conditions from wttr.in — no API key required.");
+            println!("    Supports city names, IATA airport codes, GPS coordinates,");
+            println!("    postal/zip codes, and Unicode location names.");
+            println!("    Ask the agent: \"What's the weather in Tulsa?\"");
+        }
         "Webhooks" => {
             println!("  Built-in:");
             println!("    HTTP endpoint for external triggers.");

src/integrations/registry.rs

@@ -672,7 +672,7 @@ pub fn all_integrations() -> Vec<IntegrationEntry> {
             name: "Weather",
             description: "Forecasts & conditions",
             category: IntegrationCategory::ToolsAutomation,
-            status_fn: |_| IntegrationStatus::ComingSoon,
+            status_fn: |_| IntegrationStatus::Active,
         },
         IntegrationEntry {
             name: "Canvas",
@@ -995,7 +995,7 @@ mod tests {
     fn shell_and_filesystem_always_active() {
         let config = Config::default();
         let entries = all_integrations();
-        for name in ["Shell", "File System"] {
+        for name in ["Shell", "File System", "Weather"] {
             let entry = entries.iter().find(|e| e.name == name).unwrap();
             assert!(
                 matches!((entry.status_fn)(&config), IntegrationStatus::Active),