refactor: drop requests dep, route all providers through lib/http urllib wrapper (#393)

Five provider modules (pinterest, threads, instagram, tiktok, youtube_yt)
and watchlist.py each carried a try/except `requests` import with parallel
urllib + requests branches. The urllib path already used the
stdlib-only wrapper at `lib/http.py` (retries, 429 handling, HTTPError).
This collapses every dual-branch into a single `http.get`/`http.post`
call and removes the `requests` dependency from `pyproject.toml`.

Also drops 4 transitive deps (urllib3, certifi, charset-normalizer, idna)
from the lockfile, leaving the skill stdlib-only at runtime.

Tests for tiktok comments and watchlist delivery were rewritten to mock
`lib.http` directly instead of the now-removed `requests` module.

Out of scope but flagged during review: the 13 surviving SC call sites
share a near-identical scaffold and would benefit from a
`http.scrapecreators_get(url, params, token, ...)` helper. Filed for a
follow-up PR rather than expanding scope here.

skills/last30days/scripts/lib/threads.py

@@ -152,35 +152,16 @@ def search_threads(
     _log(f"Searching for '{core_topic}' (depth={depth}, limit={config['results']})")
 
     try:
-        import requests as _requests
-    except ImportError:
-        _requests = None
-
-    if not _requests:
-        _log("requests library not installed, falling back to urllib")
-        try:
-            from urllib.parse import urlencode
-            params = urlencode({"keyword": core_topic})
-            url = f"{SCRAPECREATORS_BASE}/search?{params}"
-            headers = http.scrapecreators_headers(token)
-            headers["User-Agent"] = http.USER_AGENT
-            data = http.get(url, headers=headers, timeout=30, retries=2)
-        except Exception as e:
-            _log(f"ScrapeCreators error (urllib): {e}")
-            return {"items": [], "error": f"{type(e).__name__}: {e}"}
-    else:
-        try:
-            resp = _requests.get(
-                f"{SCRAPECREATORS_BASE}/search",
-                params={"keyword": core_topic},
-                headers=http.scrapecreators_headers(token),
-                timeout=30,
-            )
-            resp.raise_for_status()
-            data = resp.json()
-        except Exception as e:
-            _log(f"ScrapeCreators error: {e}")
-            return {"items": [], "error": f"{type(e).__name__}: {e}"}
+        data = http.get(
+            f"{SCRAPECREATORS_BASE}/search",
+            params={"keyword": core_topic},
+            headers=http.scrapecreators_headers(token),
+            timeout=30,
+            retries=2,
+        )
+    except Exception as e:
+        _log(f"ScrapeCreators error: {e}")
+        return {"items": [], "error": f"{type(e).__name__}: {e}"}
 
     # Extract items from response (try common SC response shapes)
     raw_items = (