docs: address review — redundancy proof for Passive, wave-2 split, re-enable Contractions

mara's review, addressed with evidence not assertions:

- Microsoft.Contractions: re-enabled per her flat disagreement, no
  argument.
- Microsoft.Passive vs write-good.Passive: she asked what the
  difference actually is. Ran both individually against the full
  docs/ tree and diffed the exact file:line:col sets -- 726/726
  identical, zero difference either direction. Genuinely redundant,
  not assumed. write-good.Passive stays enabled (agreed base style),
  Microsoft.Passive drops as the literal duplicate.
- write-good.Passive: she disputed my invented examples (correctly --
  a clean single-actor rewrite does read better active). Pulled 10
  real hits from the actual docs tree instead of inventing more
  sentences; most have a generic/implicit actor where passive reads
  naturally, not a clear active-voice win. Re-enabled per the
  redundancy point above rather than disabled as "mostly noise".
- Microsoft.Dashes: same outcome (stays disabled, retrofitting ~2000
  existing occurrences is out of scope here) but the reasoning was
  wrong -- not a "deliberate convention", an incidental one nobody
  chose. Rewritten.
- Microsoft.Adverbs, alex.ProfanityUnlikely, write-good.E-Prime,
  Microsoft.HeadingAcronyms: moved to an explicit "wave 2 candidates"
  section -- disabled for this rollout, not dismissed. Each needs a
  real false-positive-rate pass or an actual rewrite pass through the
  flagged instances before a permanent call.
- Dropped the .vale.ini header's pointer to "the PR description" for
  rationale -- not durable/visible enough as a reference from a file
  that lives in the repo. Rationale is now fully inline per rule.

1069 more hits than the previous round (726 write-good.Passive + 343
Contractions, Microsoft.Passive's 726 removed) -- 1732 total across 50
files.

.forgejo/workflows/ci.yml

@@ -67,3 +67,23 @@ jobs:
         # lint above pushes people toward, so the pointers need a gate of
         # their own. See scripts/check-doc-refs.sh.
         run: sh scripts/check-doc-refs.sh
+
+  prose-lint:
+    name: prose lint (vale)
+    runs-on: [hive-ci]
+    # A `vale sync` + full docs/ run took under a minute in testing.
+    timeout-minutes: 5
+    steps:
+      - uses: actions/checkout@v3
+      - name: lint
+        # Styles (Microsoft + alex + write-good, named in .vale.ini's
+        # `Packages` line) are fetched fresh from the Vale Package Hub each
+        # run rather than vendored, so this job always lints against
+        # upstream's current rules. Failing red on a hit is intentional --
+        # the existing docs/ tree has a real backlog against these rules
+        # (663 hits as of this writing), so this job starts out red on
+        # unrelated PRs until that backlog is worked down. Not (yet) wired
+        # into branch protection as a required check, so a red result here
+        # doesn't block a merge -- opting it into required-check status is
+        # a separate, later call.
+        run: XDG_DATA_HOME="$PWD/.vale-data" nix shell nixpkgs#vale --command sh -c 'vale sync && vale docs'