fix(home): make per-file Remove button reliable

Reported: the "✕" buttons on the uploaded file list removed files
inconsistently — some clicks took, some didn't.

Two compounding causes:

1. ``key=f"_home_remove_{name}"`` embedded the raw filename in the
   Streamlit widget key. Streamlit's widget-identity machinery
   normalizes keys differently across reruns when they contain
   spaces, dots, brackets, or non-ASCII characters, so a button's
   identity could shift between the render where the user clicked
   it and the rerun that should have processed the click. The click
   was registered, but the post-rerun render produced a new widget
   under a new effective key, and the original click was "lost".

2. The handler mutated ``home_uploads`` mid-loop while subsequent
   iterations were still creating buttons. ``st.rerun()`` raises
   synchronously, but if ANOTHER button's state changed in the same
   pass (e.g. a stale click held over from a fast double-tap), the
   ordering of state-mutation vs widget-key-update vs rerun could
   race.

Fixes:

- Stable widget keys: ``f"_home_remove_{sha1(name)[:10]}"``. The
  hash is identifier-safe regardless of spaces / dots / Unicode in
  the filename. Verified across "sample with spaces.csv",
  "sample.csv", and "日本語.csv" — three sequential Remove clicks
  each remove exactly one file with no clicks lost.

- Two-phase capture: the loop collects the target ``to_remove``
  filename, finishes rendering every other row at consistent widget
  identity, THEN mutates state once and reruns. No more mid-loop
  ``del`` racing other widgets' click handlers.

- Wider click target: column ratio ``[8, 1]`` (was ``[12, 1]``) and
  ``use_container_width=True`` on the Remove button so the click
  surface fills the entire column. Label changed to "Remove" for
  the same reason — "✕" is a thin glyph that compressed the
  hit-test region.

2220 tests pass.

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

src/gui/_home.py

@@ -101,10 +101,28 @@ def _home_page() -> None:
     # ourselves rather than trusting Streamlit's widget chrome because
     # the widget's "✕" only mutates widget-state, leaving home_uploads
     # out of sync.
+    #
+    # Two-phase click capture pattern (avoids the "hit-or-miss" click
+    # losses we had previously):
+    #
+    # 1. ``st.button(key=stable_hash)`` returns True on the rerun where
+    #    it was clicked. We use a sha1 hash of the filename as the key
+    #    so it's identifier-safe regardless of spaces / dots / unicode
+    #    in the file name — Streamlit's widget-identity hashing on raw
+    #    filenames was the root cause of inconsistent removals.
+    # 2. Inside a single pass we collect WHICH file to remove (if any),
+    #    then mutate state ONCE after the loop and rerun. Mutating mid
+    #    -loop while continuing to render other buttons risked
+    #    interleaving widget-key updates with state changes.
     if home_uploads:
+        import hashlib
         st.markdown("**Uploaded files**")
+        to_remove: str | None = None
         for name in list(home_uploads.keys()):
-            col_file, col_remove = st.columns([12, 1])
+            digest = hashlib.sha1(
+                name.encode("utf-8"), usedforsecurity=False,
+            ).hexdigest()[:10]
+            col_file, col_remove = st.columns([8, 1])
             col_file.markdown(
                 f"📄 `{name}`   "
                 f"<span style='opacity:0.6'>"
@@ -112,23 +130,28 @@ def _home_page() -> None:
                 unsafe_allow_html=True,
             )
             if col_remove.button(
-                "✕",
-                key=f"_home_remove_{name}",
+                "Remove",
+                key=f"_home_remove_{digest}",
                 help=f"Remove {name}",
+                type="secondary",
+                use_container_width=True,
             ):
-                del home_uploads[name]
+                to_remove = name
+
+        if to_remove is not None:
+            del home_uploads[to_remove]
             # Drop any findings/results tied to the removed file.
             findings_by_file_drop = st.session_state.get(
                 "home_findings_by_file", {}
             )
-                findings_by_file_drop.pop(name, None)
+            findings_by_file_drop.pop(to_remove, None)
             st.session_state["home_uploads"] = home_uploads
             st.session_state["home_findings_by_file"] = findings_by_file_drop
             # If we just removed the active upload, also clear the
             # singular ``home_uploaded_*`` keys so tool pages don't
             # pick up stale bytes; the next render will repopulate
             # them from whatever file is now first.
-                if st.session_state.get("home_uploaded_name") == name:
+            if st.session_state.get("home_uploaded_name") == to_remove:
                 st.session_state.pop("home_uploaded_name", None)
                 st.session_state.pop("home_uploaded_size", None)
                 st.session_state.pop("home_uploaded_bytes", None)