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/pages/6_Outlier_Detector.py

@@ -14,6 +14,7 @@ if str(_project_root) not in sys.path:
 from src.gui.components import (
     back_to_home_link,
     render_sticky_footer,
+    render_tool_header,
     hide_streamlit_chrome,
     require_feature_or_render_upgrade,
 )
@@ -31,8 +32,7 @@ require_feature_or_render_upgrade(FeatureFlag.OUTLIER_DETECTOR)
 # Header
 # ---------------------------------------------------------------------------
 
-st.title(t("tools.06_outlier_detector.page_title"))
-st.caption(t("tools.06_outlier_detector.page_caption"))
+render_tool_header("06_outlier_detector")
 
 st.info("This tool is under development.")