Fix spawn placement under the top bar, add per-window minimum sizes, and clean up maximize

Four reports after restarting into today's build, with a screenshot. The
screenshot was measured, not eyeballed: top bar y=0..29, a 4px accent border
at y=30..33, titlebar from y=34, bottom border at y=1027..1030, and 49px of
bare desktop below it.

Windows spawning too close to the top bar. A remembered position was
validated only by asking whether it landed on some monitor's full_geometry,
which includes the strip a top bar reserves, so an app whose remembered y was
small reopened with its titlebar under the bar. That is why it was
"sometimes": it depended on the stored value, and the live store holds
wezterm at y=44 and firefox at y=69 against a 30px bar. Remembered positions
are now clamped into the monitor's usable area.

Placement not surviving a logout. Window memory does persist, but five of the
eleven entries in the live store were saved with a second monitor attached,
at x >= 2000. Those points match no current monitor and were discarded
outright, falling back to a fresh cascade, so those apps appeared to remember
nothing. Such a position is now clamped onto a monitor that exists instead.

Per-window minimum sizes. One global floor is wrong in both directions.
Three sources now, in increasing precedence: the global floor, the client's
own declared minimum (xdg_toplevel.set_min_size or ICCCM hints), and a
min_width/min_height window rule overriding both. A rule wins permanently --
the backend refreshes the client's declared minimum on every decoration
redraw and must not undo a deliberate override.

Maximize, three faults in one report. A maximized window now draws no
border: its edges are the screen's edges, and the only place maximize stops
short is the bar strip, which is exactly where the measured line was.
maximize_geometry_for no longer subtracts a bottom-anchored dock's exclusive
zone, so maximize runs to the bottom of the screen and the dock floats over
it; top, left and right are still honoured.
general.maximize_covers_dock = false restores the old behaviour. With the
border gone the window sits flush under the bar instead of with an accent
line crowding it.

Verified: seven new tests on the real numbers from the live store, and
maximize geometry measured live in a nested instance (a window maximized on a
split half reports exactly that half's rect). NOT confirmed on screen: the
border removal and the dock behaviour - the nested backend has no bar or
dock to reserve a zone, and an attempt to check the border produced a failing
control, since srd set border_width only affects windows created after it.

515 tests pass, clippy clean.

1 files changed, 21 insertions, 0 deletions

diff --git a/crates/core/src/window.rs b/crates/core/src/window.rs
index ee9fd23..272d772 100644
--- a/crates/core/src/window.rs
+++ b/crates/core/src/window.rs
@@ -197,6 +197,25 @@ pub struct Window {
     /// (GNOME, KDE, Windows) hides or disables it in exactly this case.
     /// Asked for as titlebars with "buttons of the program/dynamic".
     pub resizable: bool,
+    /// This window's own minimum size, in physical pixels. Defaults to the
+    /// global [`crate::placement::MIN_WINDOW_WIDTH`]/`MIN_WINDOW_HEIGHT`.
+    ///
+    /// Two sources, in order of precedence: a `min_size` window rule, and
+    /// the client's own declared minimum (`xdg_toplevel.set_min_size`, or
+    /// an XWayland window's ICCCM size hints), which the backend fills in
+    /// the same way it fills `resizable`.
+    ///
+    /// One global minimum for every window is wrong in both directions: it
+    /// is far too small for an application that needs room to lay out at
+    /// all, and too large for a small utility or palette window. Asked for
+    /// as "different windows should have minimum sizes depending on what
+    /// window is".
+    pub min_size: (u32, u32),
+    /// Set when `min_size` came from a `min_size` window rule rather than
+    /// from the client or the default. The backend refreshes a client's
+    /// declared minimum on every decoration redraw, and must not overwrite
+    /// a deliberate rule with it.
+    pub min_size_from_rule: bool,
     /// `decorated`'s value from just before entering fullscreen, restored
     /// on exit - see `WindowManager::toggle_fullscreen`'s doc comment on
     /// why this can't just hardcode `true` back.
@@ -302,6 +321,8 @@ impl Window {
             decorated: true,
             is_dialog: false,
             resizable: true,
+            min_size: (crate::placement::MIN_WINDOW_WIDTH, crate::placement::MIN_WINDOW_HEIGHT),
+            min_size_from_rule: false,
             restore_decorated: None,
             floating: false,
             minimized: false,