feat: hot-activate WASM channels, channel-first prompts, unified artifact resolution (#297)

* refactor: unify WASM artifact resolution into registry/artifacts.rs

Consolidate duplicated WASM find/build/install logic from 5+ files into
a single src/registry/artifacts.rs module. This fixes two bugs:
- registry/installer.rs now respects CARGO_TARGET_DIR (was hardcoded)
- channels/wasm/bundled.rs now searches all WASM triples (was wasip2 only)

Also includes: extension manager hot-activation for WASM channels,
extension guidance in LLM prompts, channel manager hot-add support,
webhook router channel lookup, and minor cleanups.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* fix: send approval prompts as messages on WASM channels (Telegram, Slack)

WASM channels mapped ApprovalNeeded status to a typing indicator,
so users on Telegram never saw tool approval prompts — the agent
got stuck in AwaitingApproval and all subsequent messages failed
with "Waiting for approval".

- Intercept ApprovalNeeded in WasmChannel::handle_status_update and
  send the prompt as an actual message via call_on_respond, showing
  tool name, description, parameters, and yes/no/always instructions
- Guard against empty LLM responses after clean_response() strips
  reasoning_content think-tags (defense-in-depth for reasoning models)
- Add reasoning_content fallback to NearAiChatProvider::complete()
  for consistency with complete_with_tools()
- Add debug logging when empty responses are suppressed
- Improve error logging for channel respond() failures
- Register WASM channel webhook routes before credential checks so
  platforms don't deactivate webhook URLs with 404s

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* fix: address PR #297 review comments

- ChannelManager::add: use async write().await instead of try_write()
- resolve_target_dir: resolve relative CARGO_TARGET_DIR against crate_dir
- install_wasm_files: log warning on capabilities copy failure
- refresh_active_channel: load capabilities file for webhook secret name
- activate_wasm_channel: validate name against path traversal
- Fix cargo fmt formatting in nearai_chat.rs

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* fix: wire up channel runtime for hot-activation and address PR review round 2

- Wire up set_channel_runtime() in main.rs so hot-activation actually works
  (with_channel_runtime was never called — hot-activation was dead code)
- Change ExtensionManager channel runtime fields to RwLock<Option<...>>
  interior mutability so set_channel_runtime(&self) works after Arc wrapping
- Fix artifact tests to use resolve_target_dir() instead of hardcoding
  "target/" (breaks when CARGO_TARGET_DIR is set)
- Fix bundled.rs build hint: cargo component build (not cargo build --target)
- Fix wasm_artifact_path doc: binary_name should not include .wasm extension

Co-Authored-By: Claude Opus 4.6 <[email protected]>

* fix: use char-aware truncation to prevent UTF-8 panic in approval prompt

&s[..77] panics on multi-byte UTF-8 (CJK, emoji). Use s.chars().take(77)
for safe truncation at character boundaries.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

---------

Co-authored-by: Claude Opus 4.6 <[email protected]>

tests/html_to_markdown.rs

@@ -27,10 +27,8 @@ fn normalize(s: &str) -> String {
 /// Normalize typographic/smart punctuation to ASCII so tests match converter output
 /// regardless of apostrophe/quote variants (e.g. U+2019 ' → U+0027 ').
 fn normalize_smart_punctuation(s: &str) -> String {
-    s.replace('\u{2019}', "'") // RIGHT SINGLE QUOTATION MARK
-        .replace('\u{2018}', "'") // LEFT SINGLE QUOTATION MARK
-        .replace('\u{201C}', "\"") // LEFT DOUBLE QUOTATION MARK
-        .replace('\u{201D}', "\"") // RIGHT DOUBLE QUOTATION MARK
+    s.replace(['\u{2019}', '\u{2018}'], "'")
+        .replace(['\u{201C}', '\u{201D}'], "\"")
 }
 
 #[test]
@@ -58,15 +56,13 @@ fn convert_test_pages_to_markdown() {
             .unwrap_or("unknown");
         let default_url = format!("https://example.com/test-pages/{}/", dir_name);
 
-        let metadata: PageMetadata = path
-            .join("metadata.json")
-            .is_file()
-            .then(|| {
-                let raw = std::fs::read_to_string(path.join("metadata.json"))
-                    .expect("read metadata.json");
-                serde_json::from_str(&raw).expect("invalid metadata.json")
-            })
-            .unwrap_or_default();
+        let metadata: PageMetadata = if path.join("metadata.json").is_file() {
+            let raw =
+                std::fs::read_to_string(path.join("metadata.json")).expect("read metadata.json");
+            serde_json::from_str(&raw).expect("invalid metadata.json")
+        } else {
+            Default::default()
+        };
 
         let url = metadata.url.as_deref().unwrap_or(&default_url).to_string();