The Telegram bot token redaction had an off-by-one bug: it searched for
the next "/" starting from the "/bot" position, which found the "/" in
"/bot" itself (offset 0) instead of the next "/" after the token.
Result: tokens were not properly redacted and the URL got corrupted with
duplicated path segments, potentially leaking secrets to logs/API responses.
Fix: search from idx+4 (after "/bot") and handle edge cases where there's
no trailing slash (token at end of URL or before query string).
Added 20 comprehensive test cases covering:
- No secrets (passthrough)
- Telegram bot tokens (various patterns)
- Query parameter secrets (token, apikey, api_key, key, secret, password)
- Multiple parameters and edge cases
