Refactor/core cleanup

…t fixes

Critical fixes:
- ericc-ch#4 Use WEB_SEARCH_FUNCTION_TOOL.function.name constant instead of hardcoded
  "web_search" string in interceptor — eliminates silent maintenance trap
- ericc-ch#9 Set tool_choice:"none" in second pass to prevent model from re-invoking
  web search, which would produce unresolvable finish_reason:"tool_calls" for
  the Anthropic client
- ericc-ch#10 Scope Path 2 preflight to only fire when the payload contains a custom
  tool whose name is in WEB_SEARCH_TOOL_NAMES — prevents firing on every
  Claude Code request (which always includes Bash/editor tools but never
  explicitly declares a web search tool)
- ericc-ch#18 Move WEB_SEARCH_FUNCTION_TOOL injection into interceptor via new
  prepareWebSearchPayload() — keeps tool injection co-located with the code
  that depends on it; handler no longer reaches into service internals

Important fixes:
- ericc-ch#1 Document rate-limit bypass in interceptor JSDoc and update startup log
  message to clarify internal calls are not counted against the rate limit
- ericc-ch#3 Simplify toolResultContent control flow — results and errors are assigned
  on every branch before buildSecondPass is called (no more nested try/catch)
- ericc-ch#6 getPreflightModel prefers cheap models (mini/flash/haiku/small heuristic)
  instead of "any model that isn't the request model"
- ericc-ch#11 Replace array index cast with Array.at() for natural undefined safety
- ericc-ch#13 Use XML delimiters in preflight prompt to prevent quote characters in
  user messages from breaking the classifier prompt (prompt injection fix)
- ericc-ch#14 Add consola.debug calls in interceptor for first/second pass payloads
  and responses so --verbose is useful for debugging web search issues
- ericc-ch#8 Add "// Web search configuration" section comment in State interface

Tests updated:
- Fix tool_choice test: second pass must use "none", not pass original value
- Add prepareWebSearchPayload tests (3 tests)
- Add Path 2 scoping tests: bash-only tools skip preflight; web_search custom
  tool fires preflight (2 tests)
- Add empty tools array test for Path 2 skip

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