Web client comments describe the code to a stranger (#6222)

Milestone 546 "Bring the repo to the comment standard (rule 32) and
compose defaults (rule 198)", step #6222 "Comment standard sweep: web
client (frontend/)".

Comments, docstrings and template notes across frontend/ now say what
the code does and the non-obvious why as present-tense facts. Issue,
task, note, milestone and family-idea references are gone, along with
narration of what used to happen: the titles index's wiki-link origin
and its once-per-session load (#5165), the card-controls overlap a
phone showed (task 2697), the M7 and M10.9 labels, and the card
unification behind the reminders lens (task 1913). Hazards stay as
facts, among them LEAVE_MS matching the editor's leave duration, the
Android client twin that must not be widened, and keeping leavers in
flow in the multi-column masonry.

62 files, comments only: a comment-stripping diff of every changed file
against HEAD is identical.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/index.html

@@ -2,12 +2,9 @@
 <html lang="en">
   <head>
     <meta charset="UTF-8" />
-    <!-- `viewport-fit=cover` is what makes `env(safe-area-inset-*)` resolve to
-         anything other than 0. It opts the page into drawing under the notch and the
-         gesture bar, so it is only safe alongside the padding that keeps content out
-         of them — see style.css (sides), the sticky header (top) and the board
-         (bottom). The two halves ship together, deliberately: turning this on alone
-         is worse than leaving it off (task 2706). -->
+    <!-- `viewport-fit=cover` makes `env(safe-area-inset-*)` non-zero and draws the page
+         under the notch and gesture bar. Only safe with the padding that keeps content
+         out of them: style.css (sides), the sticky header (top) and the board (bottom). -->
     <meta name="viewport" content="width=device-width, initial-scale=1.0, viewport-fit=cover" />
     <meta name="theme-color" content="#F5C518" />
     <meta