feat(gui): inline Help popover next to every tool's title

Adds a contextual Help button on each detail page, right of the title.
Clicking it opens a Streamlit popover with a one-shot how-to: when to
use, numbered steps, before→after examples, and an optional one-line
tip. Designed to be scannable — no paragraph prose.

Implementation:
- New ``render_tool_header(tool_id)`` helper in components replaces the
  bare ``st.title(...) + st.caption(...)`` block on each of the 11 tool
  pages. Title in the wide column, popover in a narrow right column;
  caption sits on its own line beneath.
- Help content is one markdown blob per tool stored in i18n under
  ``tools.<id>.help_md`` (en + es). Editors can tweak copy without
  touching Python.
- ``help.button_label`` and ``help.missing_body`` keys added to both
  packs for the popover trigger and the empty-tool fallback.

All 11 tool pages now use the same header pattern — including the
PDF Extractor and Reconciler which previously had hardcoded title/
caption pairs.

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

src/gui/components/__init__.py

@@ -48,6 +48,7 @@ __all__ = [
     # Shared chrome / pickup
     "back_to_home_link",
     "render_sticky_footer",
+    "render_tool_header",
     "hide_streamlit_chrome",
     "html_download_button",
     "local_download_button",

src/gui/components/_legacy.py

@@ -2042,6 +2042,40 @@ a[data-testid="stPageLink-NavLink"][href*="close"] {
     )
 
 
+def render_tool_header(tool_id: str) -> None:
+    """Title row with an inline Help popover anchored to the right.
+
+    Replaces the bare ``st.title(...)`` + ``st.caption(...)`` block on
+    each tool page. Help content is one markdown blob per tool in the
+    i18n pack (``tools.<id>.help_md``) so editors can tweak copy without
+    touching Python. The popover is anchored next to the title rather
+    than the caption so it reads as part of the page header.
+
+    Layout: ``[title | help button]`` over ``[caption]``. The help
+    column is narrow; the title gets the rest. Vertical alignment is
+    left to Streamlit's column default (top) — works on 1.35+ without
+    the ``vertical_alignment`` kwarg that landed later.
+    """
+    col_title, col_help = st.columns([10, 1])
+    with col_title:
+        st.title(_t(f"tools.{tool_id}.page_title"))
+    with col_help:
+        # Spacer pushes the popover button down so it sits closer to
+        # the title's baseline than to its top — without the spacer the
+        # button floats above the big title text.
+        st.write("")
+        body = _t(f"tools.{tool_id}.help_md")
+        if body.startswith("tools."):
+            body = _t("help.missing_body")
+        with st.popover(
+            _t("help.button_label"),
+            icon=":material/help_outline:",
+            use_container_width=True,
+        ):
+            st.markdown(body)
+    st.caption(_t(f"tools.{tool_id}.page_caption"))
+
+
 def _render_sticky_footer_DISABLED() -> None:
     """Slim fixed-position footer at the bottom of the viewport.