fix(repo): make the deploy guard fire, and record the deletion of musher-dev/specs

[justinmerrell]

Closes #51. Unblocks the repository half of #56.

The deploy guard never fired

taskfiles/build.Taskfile.yml guarded site:deploy with
requires: vars: [CLOUDFLARE_API_TOKEN, CLOUDFLARE_ACCOUNT_ID], and both
pages.yml and ADR 0012 §6 state that this "refuses to run without both, so a
missing secret fails the job instead of deploying anonymously". It does not.
GitHub Actions defines an env: key whose secret is missing — as an empty
string — and Task counts empty as set. Reproduced against Task 3.52.0, the
version CI pins:

$ CLOUDFLARE_API_TOKEN= CLOUDFLARE_ACCOUNT_ID= task site:deploy --dry
task: [site:deploy] .../wrangler pages deploy site --project-name=musher-schemas --branch=main

$ env -u CLOUDFLARE_API_TOKEN -u CLOUDFLARE_ACCOUNT_ID task site:deploy --dry
task: Task "site:deploy" cancelled because it is missing required variables: ...

The guard fired only when the variables were genuinely undefined, which is the
one state CI never produces. Both failed Pages runs on main show the
consequence: wrangler ran and emitted its own error.

A precondition testing for emptiness now fires in all three failure states —
unset, empty, and one of the two missing — and passes only when both are
non-empty. pages.yml's comment gains the reason, because the failure mode is
not visible from the file that depends on it.

musher-dev/specs is deleted, not archived

ADR 0012 §5 decided the superseded repository would be archived, reasoning that
deletion 404s every inbound reference including ADR 0001's own account of why
this repository exists. That reasoning is not withdrawn. What changed is that
the harm it was weighed against went live: musher-dev/infra#336 has merged and
applied, schemas.musher.dev resolves, and the archived repository's README
still advertises URLs on that hostname for the bundle-definition schema the
platform no longer ships.

ADR 0014 supersedes §5, states the cost rather than mitigating it away, and
closes ADR 0012 follow-up 2 by dropping specs from the organisation's
pr-workflow ruleset (14207433). Per #51's "Not doing", spec is not
added in its place.

ADR 0001 and ADR 0012 are left exactly as written. An accepted ADR records what
was decided and why; editing one to hide a dead link would cost more than the
dead link does. The four references this repository holds to the deleted
repository will 404, and ADR 0014 says so under Consequences.

Out of scope, and still yours

Setting CLOUDFLARE_API_TOKEN and CLOUDFLARE_ACCOUNT_ID (#56) and deleting
the repository itself. Neither can be done from here.

Verification

task check passes. The guard was exercised in all four states:

CLOUDFLARE_API_TOKEN	CLOUDFLARE_ACCOUNT_ID	Result
unset	unset	refused
empty	empty	refused — the CI case, which previously passed
set	empty	refused
set	set	reaches wrangler

🤖 Generated with Claude Code