fix(build): self-heal stale build.ninja + bump 0.0.58

[Sunrisepeak]

Problem

After a dependency package under ~/.mcpp/registry/data/xpkgs/ is
reinstalled/moved but keeps the same version string, mcpp build fails:

ninja: error: '.../cmdline-0.0.1/src/parse.cppm', needed by 'obj/parse.m.o',
       missing and no known rule to make it

The file actually exists — the cached build.ninja is stale. The build
fingerprint doesn't cover registry dep state (dependencyLockHash is empty),
so fp.hex/outputDir are unchanged and try_fast_build reuses the old
graph. That ninja error isn't recognized as "stale", so it hard-fails and the
user has to run mcpp clean by hand.

Fix

Add "missing and no known rule to make" to is_stale_ninja_failure
(src/build/execute.cppm). On that signature, try_fast_build returns
nullopt → the same mcpp build invocation drops to a full graph
regeneration, rewrites build.ninja against the current dep state, and
proceeds. No more manual mcpp clean.

Folding registry dep state into the fingerprint (to skip the regen entirely)
is a larger, riskier follow-up — tracked in
.agents/docs/2026-06-22-mcpp-followups-design.md §T-j.

Version bump → 0.0.58

This is the last PR of the 5-PR follow-up batch, so it carries the version
bump (fingerprint.cppm MCPP_VERSION + mcpp.toml) for the release that
ships:

• fix(scanner): skip raw-string-literal bodies when detecting imports #138 scanner raw-string fix
• feat(xlings): show progress during silent bootstrap installs + fetching-index status #139 first-run progress visibility
• fix(toolchain): list '*' reflects effective project-aware toolchain #140 toolchain effective-resolution
• feat(doctor): detect missing toolchain runtime deps / dangling subos symlinks #141 doctor runtime-dep check
• this build.ninja self-heal

Merge this PR last.

Test

mcpp build + mcpp test green (22 passed), v0.0.58 compiles clean.