fix(ci): drop invalid job-level timeout-minutes from reusable-workflow calls

A timeout-minutes: key was set on one or more jobs that call a reusable
workflow via uses:. GitHub does not permit that key on a workflow_call job, so
it rejected the file at parse time — the workflow failed instantly (0s) on
every push and never ran. The standards *-reusable.yml workflows already
declare timeout-minutes on their internal jobs, so the caller key was
redundant as well as invalid.

Files: .github/workflows/mirror.yml .github/workflows/rust-ci.yml .github/workflows/secret-scanner.yml

Verified with actionlint (real tool): no "timeout-minutes is not available"
findings remain.

Part of the estate-wide CI cleanup (84 repos; reference hyperpolymath/gitbot-fleet#374).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: hyperpolymath

.github/workflows/mirror.yml

@@ -9,5 +9,4 @@ permissions:
 jobs:
   mirror:
     uses: hyperpolymath/standards/.github/workflows/mirror-reusable.yml@d135b05bfc647d0c0fbfedc7e80f37ea50f49236
-    timeout-minutes: 10
     secrets: inherit

.github/workflows/rust-ci.yml

@@ -12,4 +12,3 @@ permissions:
 jobs:
   rust-ci:
     uses: hyperpolymath/standards/.github/workflows/rust-ci-reusable.yml@412a7031577112b31ee287cc6060179d638d6500
-    timeout-minutes: 10

.github/workflows/secret-scanner.yml

@@ -12,7 +12,6 @@ permissions:
 jobs:
   scan:
     uses: hyperpolymath/standards/.github/workflows/secret-scanner-reusable.yml@d135b05bfc647d0c0fbfedc7e80f37ea50f49236
-    timeout-minutes: 10
     secrets: inherit
   trufflehog:
     runs-on: ubuntu-latest