fix(dbmate-tool): default --version to all so a bare run migrates every version

[breken-ai]

What kind of change does this PR introduce?

Bug fix (developer tooling: nix run .#dbmate-tool).

What is the current behavior?

nix/packages/dbmate-tool.nix sets the default to PSQL_VERSION="ALL", but the dispatch at the bottom checks if [ "$PSQL_VERSION" == "all" ]. A run without --version therefore skips the all-versions loop and takes the single-version path with the literal version ALL:

Migrating to PostgreSQL version ALL
nix build --no-link github:supabase/postgres#psql_ALL/bin --json   -> no such attribute, the tool exits

That breaks the documented default: --help and migrations/README.md both say --version "defaults to --version all", and the first README example is a bare nix run .#dbmate-tool. Passing --version all explicitly works, which is why CI (it always passes --version <major>) never saw this. The mismatch dates back to the tool's first version in #1316.

What is the new behavior?

The default is now all, which matches the dispatch. A bare nix run .#dbmate-tool runs every version listed in ansible/vars.yml postgres_major (15, 17, orioledb-17), as documented. Explicit --version values behave exactly as before.

Additional context

How I tested it: I don't have Nix on this machine, so I rendered the writeShellApplication text into a plain bash script and ran it with errexit/nounset/pipefail, like writeShellApplication does. I used a stub nix that logs its arguments and only knows the real psql_15/17/orioledb-17 attributes, and a stub yq that reads the real ansible/vars.yml.

• develop, no --version: Migrating to PostgreSQL version ALL, then nix build ...#psql_ALL/bin and exit 1
• this branch, no --version: Migrating to PostgreSQL version 15, then nix build ...#psql_15/bin (the all-versions loop)
• this branch, --version 17: nix build ...#psql_17/bin, same as before

It is a one-line change inside the script string, so nixfmt is unaffected.

This PR was prepared by an AI agent (Claude) working for breken-ai. I reproduced the bug and checked the fix as described above, and I'm happy to change anything.

[imor]

Closing as this is 100% AI generated.