feat!: XDG directory layout via VpDirs - #2346

Replace get_vp_home / the monolithic home module with VpDirs: category
roots (bin, data, cache, config, state) come from an ordered resolution
chain in dirs/resolution.rs (legacy Exist-gated grandfathering, VP_* and
XDG Set overrides, then platform defaults), and first-level data subdirs
(current, js_runtime, package_manager, packages, bins) are pure joins.
Files and deeper trees stay with their features.

Wire EnvConfig so test_guard/for_test_with_home isolate install roots
without process-env leaks. Groundwork for voidzero-dev#827.

Replace every get_vp_home()-era dependency with EnvConfig::get().dirs.
Business directory helpers stay in their owning modules but are
reimplemented on the category roots, so no call site constructs install
paths ad hoc.

- env setup scripts re-export the captured layout overrides
  (EnvConfig::env_exports) instead of hardcoding a VP_HOME line;
  vp-use.cmd does the same on Windows
- env doctor reports all five category roots; bin/config are hard
  errors when missing, data/cache/state are reported as lazily created
- implode deletes the deduped {data, cache, config, state} roots and
  removes only vp-owned files from the bin directory, which may be a
  shared ~/.local/bin
- upgrade-check cache moves to the state root; shim resolve cache
  lives under the cache root

Fresh installs write the split platform roots; an existing ~/.vite-plus
or --install-dir stays on the monolithic tree. Directory env vars stay
owned by EnvConfig: vp-setup reads only EnvConfig::get().dirs, and a
local vp binary reports those roots via VP_DUMP_DIRS so install.sh /
install.ps1 / install-global-cli do not re-implement the chain.

- Unix shims target <DATA>/current/bin/vp after env setup --refresh
- Windows trampoline finds ../current or ../data/current without
  reading VP_HOME / VP_*_DIR
- Standalone-install CI pins VP_HOME for published pre-split CLIs and
  adds a local-build job for fresh split + grandfather

CI still looks for $HOME/.vite-plus/bin/vp after bootstrap-cli:ci.
Create that directory before EnvConfig resolves so the existing-install
probe wins, without setting VP_HOME.

Also clone rolldown/vite before the local-build layout job so
`cargo build -p vp_global_cli` can load the workspace.

The test fetches the Node version index after scanning the cache. Without
an EnvConfig::with_vars_async pin it can observe a concurrent test's
VP_NODE_DIST_MIRROR=https://mirror.example/node and fail DNS lookup.

Implode only removes shims that resolve to this install's vp. Generated
env files persist resolved VP_*_DIR. Legacy Windows wrappers pin VP_HOME
to the data root. Upgrade-check cache moves to <CACHE>. Org-tarball cache
goes through EnvConfig.

Independent VP_BIN_DIR / VP_DATA_DIR installs cannot be found by
sibling-path probing. Write <name>.shim next to each trampoline and
resolve vp.exe from that pointer. Align install.ps1 with Windows
known folders so installer roots match EnvConfig.

install.sh now links <BIN>/vp to the absolute
<DATA>/current/bin/vp path. The grandfather layout job still
asserted the old relative ../current/bin/vp target.

Avoid the PowerShell 5 $HOME collision in install.ps1. Require a
matching <name>.shim before implode deletes Windows exes. Pin
VP_HOME from the trampoline for single-root bin/data layouts.
Write JetBrains node paths from getVpDirs(). Persist VP_HOME in
dir_envs only when it is an absolute path.

Pre-split binaries resolve every path from VP_HOME (default ~/.vite-plus),
so installing one into split roots produced a broken PATH vp next to a
half-built legacy tree while still exiting 0. install.sh, install.ps1, and
vp-setup now probe the downloaded payload with VP_DUMP_DIRS=1 before the
layout is final: a split-aware binary reports its category roots, which the
installer adopts verbatim, and a binary that cannot answer falls back to
the monolithic root (VP_HOME or ~/.vite-plus) with a notice. This also
keeps fresh installs of latest working until the first split-aware release
ships.

vp-setup returns the effective directories for its success summary and
removes the abandoned split data root that its managed node/pnpm downloads
land in when this run created it.

New test-install-sh-old-version (Linux, macOS) and
test-install-ps1-old-version (Windows) CI jobs install 0.2.9 with no
VP_HOME and assert the legacy layout and working PATH-resolved commands.
The mechanism is documented in rfcs/directory-layout.md and the VP_VERSION
entry of docs/guide/installer-env-vars.md.

with_vars_home_yields_split_layout pinned only HOME/USERPROFILE, so a
shell that exports VP_HOME (vp's own env script does) or XDG_* resolved
those overrides instead of the platform tail and failed. Clear every
layout override var in the test.

On a split install, vp upgrade installed a pre-split payload into the
split data root and activated it; the old binary then moved config,
runtimes, and later upgrades to ~/.vite-plus while the split PATH entries
kept serving the old version.

Gate the target version before the download: below 0.3.0 is rejected
with a message that names the minimum version, preview builds
(0.0.0-commit.<sha>) are allowed, and monolithic installs (VP_HOME pin
or grandfathered ~/.vite-plus) accept every release, so the existing CI
upgrade tests keep their targets. The upgrade path uses a version gate,
not the payload probe: the running binary is split-aware by definition,
so the boundary is a fixed release number.

Move probe_payload_dirs into vp_setup with unit tests; vp-setup keeps
using it, the upgrade path does not.