* fix(install): rewrite relative skill links for injected ecc namespace
Skill and rule markdown is byte-copied during a claude install, but the
home/project adapters inject an `ecc/` namespace segment
(skills/<id> -> skills/ecc/<id>, rules/<x> -> rules/ecc/<x>). Source-relative
links such as `../../rules/react/hooks.md` therefore broke after install: the
extra level changed what `../..` resolved to, and the link target itself moved
under rules/ecc/.
Rewrite relative links in namespaced markdown so they resolve to the file's
actual installed location, derived from the plan's own file placements (no
hardcoded namespace literal, so the links cannot drift from where files land).
Non-namespacing adapters and links to non-installed targets are left untouched;
URLs, anchors, absolute paths, and fenced code blocks are never rewritten.
Fixes#2340
* fix(install): keep non-namespaced markdown on the byte-for-byte copy path
Address review feedback: the markdown branch in applyInstallPlan diverted every
copy-file markdown operation through read+rewrite+write, so identity-mapped
markdown (source path == install path, no namespace injected) lost byte-for-byte
content and source mode bits even though no link rewrite was needed.
Gate the rewrite on isNamespacedSource() so only files whose install path
actually changed (e.g. skills/x -> skills/ecc/x) leave the copyFileSync path;
everything else is copied verbatim as before.
* test(install): emit failure stack in the link-rewrite test runner
Address review feedback: the local test() harness logged only error.message,
so a failing assertion lost its source line and diff. Print error.stack on
stderr on failure so broken rewrite cases stay diagnosable.
0a926b45ba