fix(#14): wire --auto flag through progress→next handoff (#148)

* fix(#14): document --auto in progress.md and wire chaining logic in next.md

The --auto flag was accepted by /gsd:progress --next --auto but silently
ignored: it was not documented in the <flags> section of progress.md and
had no handling in the next.md show_and_execute step, so it was dropped
at the handoff boundary and never produced step chaining.

- Add --auto and --next --auto entries to progress.md <flags>
- Update progress.md <process> to explicitly list --auto as a passthrough arg
- Add --auto chaining logic to next.md show_and_execute: after each step
  completes, re-invoke /gsd:progress --next --auto until milestone complete
  or a blocking decision is required
- Add regression test (4 assertions) covering all three fix points

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* fix(#14): bump lint-test-file-count progress ceiling for bug-14 test

bug-14-progress-auto-flag-dropped.test.cjs resolves to the "progress"
effective prefix and legitimately grows the cluster to 6.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

* chore(#14): add changeset fragment

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

* fix(#14): address review feedback — differentiate duplicate tests, scope assertions to specific blocks

Test 2 now extracts the <process> block and asserts --auto within it,
distinguishing it from test 1's <flags>-level check. Remaining assertions
use semantic token matches (--auto, --next --auto) that are robust to
benign reformatting.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

.changeset/14-progress-auto-flag.md

@@ -0,0 +1,5 @@
+---
+type: Fixed
+pr: 148
+---
+The `--auto` flag is now wired through the `/gsd:progress` → `/gsd:next` handoff so that chaining these commands works without requiring the flag to be re-supplied manually.