Fix multiple-installs false positives for asdf and mise shims

[gtsiolis]

Motivation

lstk warns about "multiple installs" whenever a version-manager shim and the install it dispatches to are both reachable on PATH, even though they are the same install — a false positive that fires on every run.

• asdf: an asdf-managed npm install is also reachable through its asdf shim.
• mise (reported by Daniel): with shim mode and PATH mode both enabled (mise's recommended mix for interactive + non-interactive sessions), ~/.local/share/mise/shims/lstk and ~/.local/share/mise/installs/<tool>/<version>/lstk both land on PATH. A mise shim is a bare symlink to the mise binary itself (argv[0] dispatch, no metadata), so neither symlink dedup nor content parsing can relate it to its install.

Changes

• Resolve asdf shim scripts back to their real install path (internal/update/installs_unix.go) by parsing the # asdf-plugin: <name> <version> comment asdf writes into each shim, before dedup runs in FindInstalls (internal/update/installs.go)
• Resolve dispatcher shims (mise): a candidate in a shims/ dir that symlink-resolves to an executable not named lstk is aliased to the first PATH candidate under the sibling installs/ tree — the same check mise itself uses to recognize its shims (is_active_mise_shim), no hardcoded tool names. A shim with no backing install on PATH (pure shim mode + e.g. a homebrew lstk) still counts, so genuine conflicts keep warning.
• Add a no-op executableAlias on Windows (installs_windows.go); mise's Windows .exe-copy shims are a known gap left out of scope
• Add unit tests TestFindInstallsDeduplicatesAsdfShimAlias, TestFindInstallsDeduplicatesMiseShimAlias, TestFindInstallsKeepsMiseShimWithoutBackingInstallOnPath and integration tests TestUpdateCheckDoesNotWarnOnAsdfShimAlias, TestUpdateCheckDoesNotWarnOnMiseShimAlias

Known limitation: mise resolves the shim's dispatch target per-invocation from its config, so a hand-pinned stale installs/<tool>/<old-version> PATH entry diverged from the configured version is deduped rather than warned. Inherent to any heuristic that doesn't execute mise; documented in the code.

Review

Human review advised — user-facing behavior with a teammate-reported case (Daniel's mise setup), and the dispatcher heuristic deserves a second pair of eyes.

Tests

New unit + integration tests reproduce both false positives and confirm they're resolved. Also verified against real installs: asdf + npm on this machine, and a real mise use github:localstack/lstk install (dual shim + PATH mode) that reproduced Daniel's warning byte-for-byte with released v0.18.0 and is silent with this branch, while a mise shim + separate binary install still warns.

Closes DEVX-1015

Co-Authored-By: Claude noreply@anthropic.com

[gtsiolis]

Cc @skyrpex because #398.

[skyrpex]

@gtsiolis thanks, didn't know about this. I thought we were fine deduping symlinks 😄