fix(project): grid tracks that cannot shrink pushed the milestone rows off-page

Reported after deploy: the milestone rows and the kanban's Done column run past
the right edge and get cut.

Both grids here use a bare `1fr`, and a `1fr` track carries an AUTO minimum —
it cannot size below its content. So one wide descendant anywhere in the
content column widens the column past the grid, everything inside inherits that
width, and `.project-view`'s `overflow-x: clip` cuts it at the page edge. The
milestone header only made it visible: it is a flex row now, so its tail
(progress track, percent, actions) sits at the right edge where the clipping
happens, where before those children stacked at the left and never reached it.

`minmax(0, 1fr)` on both, plus `min-width: 0` on the content area — a grid
item's default `min-width: auto` refuses to shrink even when its track will,
so the two halves are needed together.

Worth naming, because it is the same property twice with opposite intent: the
header nav was fixed two commits ago by RELYING on the auto minimum, so neither
side could be squeezed under its content and the pill bar stays centred. Here
that same behaviour is the defect. `1fr` is not a neutral default — it is a
statement that the track may not shrink.

I could not isolate which descendant was the wide one by reading, and said so
rather than guessing at it; this is the structural fix, which holds whichever
of the candidates it was.

Not changed: RulesView's `280px 300px 1fr` is the same shape and a plausible
latent instance, but nothing has reported it and I have not seen that surface
misbehave. Guessing at unreported layouts is how eleven fixes become eleven
regressions.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UaYUaouG9jjhATyuxCKrQs

frontend/src/views/ProjectView.vue

@@ -956,13 +956,25 @@ async function confirmDelete() {
 .stat-notes     { background: color-mix(in srgb, var(--color-primary) 8%, transparent); color: var(--color-primary); border-color: color-mix(in srgb, var(--color-primary) 22%, transparent); }
 
 /* ── Two-column body ─────────────────────────────────────────── */
+/* `minmax(0, 1fr)`, not `1fr`. A bare `1fr` track has an AUTO minimum, so it
+   cannot shrink below its content — one wide descendant anywhere in the
+   content column widens the whole column past the grid, and everything inside
+   it then overflows the page and gets cut by `.project-view`'s
+   `overflow-x: clip`.
+   This is the same property the header nav relies on and wants (neither side
+   squeezed under its content); here it is exactly wrong, because the column
+   holds a kanban whose own tracks push outward. `min-width: 0` on the item is
+   the twin half — a grid item's default `min-width: auto` refuses to shrink
+   even when its track will. */
 .project-body {
   display: grid;
-  grid-template-columns: 248px 1fr;
+  grid-template-columns: 248px minmax(0, 1fr);
   gap: 1.25rem;
   align-items: start;
 }
 
+.content-area { min-width: 0; }
+
 /* ── Edit panel ──────────────────────────────────────────────── */
 .edit-panel {
   background: var(--color-bg-card);
@@ -1190,7 +1202,10 @@ async function confirmDelete() {
 /* ── Kanban ──────────────────────────────────────────────────── */
 .kanban {
   display: grid;
-  grid-template-columns: repeat(3, 1fr);
+  /* Same reason as .project-body: three auto-minimum tracks add up to more
+     than the column when a card title or a column header won't compress, and
+     the excess pushes the whole milestone card wider than the page. */
+  grid-template-columns: repeat(3, minmax(0, 1fr));
   gap: 0.75rem;
   align-items: start;
   padding: 0.75rem;