Make installer exit 0 mean the host integration actually works

[MongLong0214]

Summary

Closes #595.

Both installers decided a host's MCP registration was fine because the config merely mentioned commitlore, or because a command string existed. A registration whose command cannot run — a directory, a non-executable file, the wrong args — was skipped as "already configured" and the installer still exited 0. The user was told the install succeeded when the integration could not work.

install exit 0 now means every requested host is either live-verified healthy, or was explicitly preserved as a healthy custom CommitLore registration.

What changed

• One shared TypeScript command, installer-hosts, invoked by both install.sh and install.ps1. The shell and PowerShell paths no longer make their own judgements — they call it and act on its result, so the two cannot drift apart.
• Ownership is exact: the wrapper path and args exactly mcp. No substring, no "the word appears", no "the directory exists".
• A custom registration is verified live by speaking MCP to it — initialize, then serverInfo, then a minimum tool set. Healthy custom registrations are preserved and reported distinctly from ones we own; dead, foreign or unverifiable ones are not ok.
• Config writes are atomic: parse → write temp → re-parse the temp → rename. An interruption before the rename leaves the original untouched, and there is a fault-injection seam that proves it rather than asserting it.
• Any requested host that fails makes the installer exit non-zero in the default mode.

Test plan

Non-zero, each asserted:

• command does not exist
• command is a directory
• our wrapper with the wrong args
• malformed / unparseable config
• host CLI that fails when invoked
• config write interrupted midway — original file intact

Zero, reported distinctly:

• a healthy registration we own

• a healthy custom registration, preserved rather than overwritten

• Negative control: restoring the presence-only check makes the dead-command case pass with exit 0 where it must exit 1

• 150 cases across installer-hosts, install-script, install-ps1 and doctor

• npx tsc --noEmit clean

• dist/ rebuilt on linux/amd64

Unverified

Windows runtime behaviour. pwsh/powershell is not available on the machine this was developed on, so install.ps1 was not executed. Its delegation to the shared command is covered structurally — same command, same JSON summary, same exit meaning — but the actual PowerShell run is unverified here and is left to the install-ps1 job on this pull request to confirm.

[github-actions]

CommitLore — record lint

Trailers: clean — 8 commits in origin/main..f9162fcfec57945ef5c492a3eb6e48c4ae60235f
Active constraints: not read — commitlore: git log --follow accepts exactly one pathspec, so renames are not followed for 12 paths; query one path at a time to follow its rename chain (12 changed paths)

_{Trailer violations fail this check. Active constraints are informational — they are what the repository already decided, not a verdict on this PR.}