fix: remove ghost pane dividers and prepare winTerm 1.1.2

[HelloThisWorld]

Summary

Fixes the ghost pane-divider lines visible in winTerm v1.1.1 and prepares the
v1.1.2 stable patch release.

Symptom: a visible divider line could render away from the actual pane
boundary — for example a full-height vertical line inside the larger
right-hand pane while the real vertical split sat farther left. Horizontal
divider overlays could likewise appear outside the split node that owns them.

Root cause: in Pane::_UpdateDividerPlacement() the drag hit target and
pointer target use a leading-edge coordinate system
(HorizontalAlignment::Left / VerticalAlignment::Top plus a margin of
dividerPosition - thickness / 2), but the visible _dividerVisual used a
primary-axis Center alignment with the same leading-edge margin. XAML
re-centers a Center-aligned element inside the space remaining after its
margin, so the visible line landed near
(container + dividerPosition) / 2 instead of dividerPosition — a ghost
line — while dragging still worked at the real boundary.

Fix (2 lines plus comments): the visible divider now uses the same
leading-edge alignment model as the pointer target — vertical dividers align
Left, horizontal dividers align Top — and stays centered on the split
position by subtracting half its own thickness in the margin. One divider now
renders exactly on each logical split boundary for all layouts, ratios, and
nesting depths; nested dividers stay confined to their owning split node.

Related issues

None filed; defect observed in the v1.1.1 release build.

Detailed changes

• src/cascadia/TerminalApp/Pane.cpp — _UpdateDividerPlacement(): vertical
  visible divider HorizontalAlignment::Center → Left; horizontal visible
  divider VerticalAlignment::Center → Top; explanatory comments. No other
  runtime change.
• scripts/winterm/test-pane-resizing.ps1 — new divider-placement regression
  boundary that isolates Pane::_UpdateDividerPlacement() without fixed line
  numbers and asserts: (1) vertical and (2) horizontal visible dividers share
  the hit target's leading-edge alignment; (3) the visible line is centered on
  dividerPosition by half its thickness; (4) the primary-axis Center
  pattern cannot silently return on any divider element; (5) the pointer
  target stays wider than the visible line; (6) _CreateDividerVisual() is
  reattached in the split-parent constructor, SwapPanes, _CloseChild,
  _Split, and Restore rebuild paths. The assertions were validated to fail
  against the v1.1.1 sources and pass against this branch.
• Version metadata 1.1.1 → 1.1.2 (package 1.1.2.0, module 1.1.2, tag
  v1.1.2, channel stable): src/winterm/Branding/version.json,
  ReleaseMetadata.h, Package-winTerm.appxmanifest, WindowsTerminal.rc,
  shell/shared/version.json, winTerm.Shell.psd1 / .psm1,
  package-shell-assets.ps1, test.ps1, verify-branding.ps1,
  verify-version.ps1, WorkspaceDescriptor.h, WorkspaceSerializer.cpp.
• Release documentation: new docs/releases/1.1.2.md (symptom, alignment
  fix, preserved behavior, unchanged schemas, 1.1.2 asset names, publisher,
  tag, and the unsigned-installer disclosure required unless a trusted
  Authenticode certificate is configured at publication); dated 1.1.2
  CHANGELOG.md entry; README.md current source version, release-note
  link, and build examples now 1.1.2 (stable /releases/latest URL and
  dynamic badge unchanged); docs/current-progress.md refreshed. The 1.1.1
  changelog entry, docs/releases/1.1.1.md, and historical references are
  preserved; StyleCop.Analyzers 1.1.118 is an unrelated NuGet version and
  was not touched.
• The release workflow's generic guarded v* trigger is unchanged; the
  expected tag continues to derive from version.json.

Preserved behavior: 1-logical-pixel idle divider, centered 12-logical-pixel
pointer target, east-west/north-south cursors, continuous live resize,
minimum-size clamping, 25/33.333/50/66.667/75% snapping, Alt bypass, Escape
and pointer-cancellation rollback, one history record per committed drag,
Undo/Redo/Balance Panes, High Contrast brushes, compact pane headers.
PaneBorderSize, DividerVisibleThickness, and DividerPointerHitThickness
are unchanged. ConPTY, the VT parser, text buffer, renderer core, Unicode
width handling, input protocols, and OpenConsole internals are untouched.
Workspace schema 2, docking model 1, shell protocol 1, theme schema 1,
package identity, winterm.exe alias, privacy boundaries, and Microsoft
Terminal coexistence are unchanged.

Validation performed

Local (Windows 11 x64, Windows PowerShell; no native MSBuild/VS toolchain on
this host):

• powershell.exe -NoLogo -NoProfile -ExecutionPolicy Bypass -File .\scripts\winterm\test-pane-resizing.ps1 -Configuration Release -Platform x64 -SourceOnly — PASS
  (compiled pane-resize tests reported SKIP as handled by the parent suite).
• powershell.exe -NoLogo -NoProfile -ExecutionPolicy Bypass -File .\scripts\winterm\test.ps1 -Suite Smoke -Configuration Release -Platform x64 — PASS
  (includes verify-version.ps1 with all 1.1.2 assertions, branding,
  shell-asset, workspace, and privacy source boundaries; compiled unit tests
  reported SKIP as not part of the Smoke suite).
• Negative test: the new divider-placement assertions were run against the
  unmodified v1.1.1 Pane.cpp and correctly failed with
  visible 'Center'; they pass on this branch.
• git diff --check — clean.

Not available locally (no Visual Studio/MSBuild/Windows SDK toolchain on this
host): native Debug/Release compilation, compiled Relevant suite, packaging,
installer/Portable lifecycle, and the manual divider acceptance matrix
(split ratios, nesting, DPI scales, High Contrast states). These are
delegated to the pull-request GitHub Actions runs of
winterm-validation.yml and winterm-full-build.yml; no manual acceptance
case is claimed here.

Release boundary

This PR only updates the intended tag metadata to v1.1.2. The actual
v1.1.2 Git tag and Release must be created only after this PR is
squash-merged, on the exact resulting main commit, so
.github/workflows/release.yml can validate the tag against
version.json. No tag is created from this branch, and no existing tag or
Release is moved or replaced.

Checklist

• The change is focused and does not include unrelated formatting.
• Tests were added or updated where appropriate.
• All tests claimed above actually ran and passed.
• User-facing behavior and limitations are documented in this repository.
• Version or schema changes include compatibility and migration notes.
• Package identity, winterm.exe, and Microsoft Terminal coexistence remain isolated.
• No command text, terminal output, clipboard content, credentials, or private paths are logged.
• New source and script files contain the appropriate MIT license header.
• I did not include generated build output, secrets, certificates, or local absolute paths.