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]>

channels-src/telegram/Cargo.toml

@@ -25,5 +25,3 @@ opt-level = "s"
 lto = true
 strip = true
 codegen-units = 1
-
-[workspace]