fix(setup): record the session-start hook as a search-path name (task 0043)

The SDK records a bare, upgrade-stable binary name only when a PATH entry
realpath-matches the execPath it is handed. From the module-relative
entrypoint that can only succeed under npm, which symlinks its bin entry
straight at it; a wrapper-based install never can, because a script that
invokes a file does not resolve to that file. So every wrapper install --
Nix, a shim, a generated .cmd -- recorded an absolute path that moves on
upgrade, and a session-start hook that cannot execute fails silently.

`setup hooks` now resolves gitea-axi on PATH itself and hands that
location to the SDK, so the bare name is recorded. A candidate qualifies
only if it resolves to the running entrypoint -- by realpath for a
symlink, or by naming it in its text for a wrapper, following the chain,
since a Nix install is two hops. A same-named binary that is some other
program does not qualify, and the absolute entrypoint path stands as the
fallback exactly as before.

The related defect on the same line goes too: the SDK recognises its hook
by finding the marker inside the recorded command, so an entrypoint path
without "gitea-axi" in it made a re-run append a duplicate rather than
update in place. `setup hooks` now prunes duplicates by matching the
exact command it records, which is independent of that command's shape
and cannot mistake another tool's hook for its own.

With the coupling gone, package.nix no longer renames its build tree; the
fast tier runs from /build/source and its idempotency test passes there.
The help text's instruction to re-run hooks after an upgrade is deleted,
having become false.

Verified against the built Nix binary and a globally npm-installed pack:
both record the bare name, both fall back to the absolute path when the
name is absent, an impostor on PATH is refused, and re-runs leave one
entry. Decision recorded as ADR 0019; ADR 0009's addendum is amended.

.claude/adr/0009-setup-command-over-postinstall.md

@@ -28,3 +28,7 @@ gitea-axi adds the same opt-in `setup hooks`; the skill remains the default `set
 
 Hooks are not the default because the hook runs the dashboard in every session in every directory, and outside a Gitea repo the dashboard errors with `REPO_NOT_FOUND` — a graceful exit-0 degradation was considered and rejected in favor of keeping the error explicit, so hook noise in non-Gitea sessions is an accepted consequence for users who opt in.
 The SDK registers the bare binary as the hook command, so the hook always runs the short dashboard tier (see ADR 0012).
+
+**Amended by [ADR 0019](0019-hook-records-search-path-name.md):** that last sentence held only for npm installs.
+The SDK records the bare name only when a `PATH` entry realpath-matches the entrypoint it is handed, which npm's symlinked `bin` satisfies and a wrapper-based install cannot.
+`setup hooks` now resolves the binary on `PATH` itself and hands that location over, so the bare name is recorded for wrapper-based installs too; the absolute entrypoint path remains the fallback when the name resolves to no install of ours.