feat(gui): 1 GB upload cap + delimiter / encoding diversity caption

Streamlit's default file_uploader footer reads "Limit 200MB per file —
CSV, TSV, XLSX, XLS" which contradicts the 1 GB efficiency target shipped
in 438bc0f and codified in docs/REQUIREMENTS.md §1.1.

Three changes:

1. .streamlit/config.toml — set [server] maxUploadSize = 1024. Footer
   now reads "Limit 1024MB per file".

2. upload_and_analyze_section (home page) — adds an explicit caption
   above the uploader stating size limit, supported formats, the four
   auto-detected delimiters, and the 13 auto-detected encodings (with
   the Review-page override as the safety net).

3. pickup_or_upload (every tool page that falls back to its own
   uploader when no home-page upload is present) — same caption,
   only rendered when the upload accepts CSV/TSV/XLSX/XLS so JSON
   schema / config uploaders aren't decorated.

Test suite: 765 passed, 17 xfailed (no regressions). Home + Review +
Deduplicator pages all serve HTTP 200 under the new config.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.streamlit/config.toml

@@ -3,3 +3,9 @@ toolbarMode = "minimal"
 
 [browser]
 gatherUsageStats = false
+
+[server]
+# Lift the default 200 MB upload cap to 1 GB so file_uploader's footer
+# reads "Limit 1024MB per file" — matches the analyzer + gate's stated
+# 1 GB efficiency target. See docs/REQUIREMENTS.md §1.1.
+maxUploadSize = 1024