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

src/gui/components/_legacy.py

@@ -981,11 +981,23 @@ def upload_and_analyze_section() -> None:
         "Optional: scan an uploaded file for data quality issues and see "
         "which tools can fix each one. Skip if you already know what you need."
     )
+    st.caption(
+        "**Up to 1 GB.** Formats: CSV, TSV, XLSX, XLS. "
+        "Delimiters auto-detected: comma, tab, semicolon, pipe. "
+        "Encodings auto-detected: UTF-8 (with/without BOM), UTF-16, "
+        "cp1252, Latin-1/9, cp1250, ISO-8859-2, cp1251, KOI8-R, "
+        "Mac Roman, Shift_JIS, GB18030, Big5, EUC-KR — and override on the Review page."
+    )
 
     uploaded = st.file_uploader(
         "Upload CSV or Excel",
         type=["csv", "tsv", "xlsx", "xls"],
         key="home_upload",
+        help=(
+            "Up to 1 GB. Comma / tab / semicolon / pipe delimiters all "
+            "auto-detected. Encoding auto-detected with override on the "
+            "Review page if needed."
+        ),
     )
     if uploaded is None:
         return
@@ -1174,6 +1186,13 @@ def pickup_or_upload(
             st.rerun()
         return _StashedUpload(name, st.session_state["home_uploaded_bytes"])
 
+    if {"csv", "tsv", "xlsx", "xls"} & set(types):
+        st.caption(
+            "Up to 1 GB. Delimiters auto-detected: comma, tab, semicolon, pipe. "
+            "Encoding auto-detected (UTF-8 / UTF-16 / cp1252 / Latin-1 family / "
+            "cp1250 / cp1251 / KOI8-R / Mac Roman / Shift_JIS / GB18030 / Big5 / "
+            "EUC-KR), with override on the Review page."
+        )
     uploaded = st.file_uploader(label, type=types, key=key, help=help)
     if uploaded is not None and st.session_state.get(override_key):
         # User has uploaded their own file on this page; clear the override