fix: show provider version when agent --version probe fails

[Drswith]

Summary

When an agent's --version probe fails (non-zero exit, crash, or unparseable output), qtx ls / qtx inspect / qtx doctor showed unknown even though the lifecycle observation already merged the provider-reported package version onto executable. The v1 inspection projector was reading the raw PATH probe (pathExecutable) for installedVersion.

This change keeps that projector thin:

• installedVersion comes from the merged executable when PATH is present, so a provider-reported version is displayed after a failed --version probe.
• inPath / installed and binary-path fields stay on PATH presence, so a provider-only version does not mark an agent as installed.
• Failed probe stdout/stderr still cannot become version evidence.

Fixes#734.

Linked Artifacts

• OpenSpec: inspect-provider-version-fallback
• Issue: [Bug]: Agent version shows "unknown" when --version probe fails even though the provider reports the exact installed version #734

Validation

• bun run memory:check
• bun run lint
• bun run format:check
• bun run typecheck
• bun run test (if behavior changed)
• bun run openspec:validate

Local results: 2191 passed, 5 skipped; OpenSpec 27/27; project memory check passed.

CI matrix on this head: lint, governance, classify, test (ubuntu-latest), test (macos-latest), and test (windows-latest) all passed. Advisory canaries also passed.

Test plan for the reported regression:

• PATH present, --version probe empty/failed, provider present+version → projector installedVersion is the provider version
• qtx ls human and JSON show that version, not unknown
• qtx inspect includes the Version row and JSON installedVersion
• qtx doctor shows the provider version, not unknown
• PATH absent + provider version still reports installed: false and omits installedVersion
• JSON field names stay frozen; payloads do not include engine or route identifiers

Release Intent

• Release: patch - bug fix

Release Summary

BEGIN_COMMIT_OVERRIDE
fix: show the provider-reported agent version when --version fails

When an installed agent's --version command crashes or exits non-zero, list, inspect, and doctor showed unknown even though the package manager already knew the installed version. Those commands now display the provider-reported version.
END_COMMIT_OVERRIDE

Docs Updated

• openspec/changes/inspect-provider-version-fallback/
• Follow-up issue or OpenSpec change created instead

Scope Check

• I did not add a new ad hoc root-level Markdown file.
• I updated the relevant issue, ADR, spec, runbook, or captured the missing doc work as follow-up.
• I did not silently expand project scope without recording it explicitly.

Closure Check

• Working tree was clean after commit.
• Branch was pushed and this PR is the active delivery artifact.
• OpenSpec change is not needed, still active until this merge, active across milestone merges by design, queued for agent-driven archive closure after completion, or already archived.
• Release is not applicable, delegated to release automation, or verified.

Notes

Product CI matrix is green. Do not tag a release in this PR; release-please should consume the user-facing patch override after merge. OpenSpec archive closure waits until this implementation PR merges and the change is archive-eligible.

JSON, aliases, exit codes, state v2, and receipts are unchanged. --json does not expose engine or route. No YAML, release-core.yml, or protect-main edits. No SDK or command expansion. Issues #133, #134, and Release Please #736 were not started.