publish: pointer apps keep their store listing; PR text lists the platforms

[TeoSlayer]

Problem

• publish-submission.sh looked for the submission's metadata.json by a path relative to the app-template checkout. It looked after cd'ing into the platform clone, so it never found the file. Every pointer app was published with a bare catalogue entry: no display name, vendor, categories, license, source or metadata page. Wallet 0.4.0's catalogue PR (pilotprotocol#529, closed) lost all of them.
• Both publish scripts built the PR's "Platforms:" list with escaped quotes inside $(...). That is a jq syntax error, so the list came out empty.

Fix

• The metadata path is absolute, resolved before the cd.
• The platform list is computed before gh pr create.

Test

TestPublishSubmissionKeepsTheStoreListing runs the real script on a two-platform pointer submission, from the repo root with a relative dir as publish-on-merge does, with gh and git push faked. It checks:

• the entry's listing fields;
• metadata_sha256 against the published metadata.json;
• the publisher pin and both bundles;
• the PR's platform list.

It fails on main, on both bugs, and passes with the fix: run in a golang container. The script needs bash 4+ (mapfile), so the test skips on macOS's bash 3.2 and runs on CI.

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