docs: fix genuine Microsoft.Contractions/Negative errors

16 of the 23 error-level hits from a full-repo vale run were real:
'is/are/does/do NOT' and bold 'not' expanded per Microsoft.Contractions,
one hyphen-as-negative-number fixed to an en dash per Microsoft.Negative
(docs/web-ui/dashboard.md's -45 deg column-header tilt).

Where the caps/bold was there for emphasis (contrasting X does this,
Y does not), kept the emphasis by bolding the contraction rather than
dropping it silently -- 'is not' -> 'isn't', 'does NOT' -> '**doesn't**',
etc.

docs/tools/swarmctl-cli.md's one genuine hit is generated -- fixed the
source doc comment in swarmctl/src/main.rs and regenerated via
'cargo run --bin swarmctl -- markdown-docs', diffed against the old
copy first to confirm only the intended line changed.

Left 7 hits unfixed, false positives from the rule matching a
substring rather than the actual pattern it names:
- 4x 'that's instead of that is': every one is the explanatory 'that
  is' idiom (~= i.e.), not a contractible subject+verb -- 'that's'
  would misparse as a demonstrative-pronoun contraction and change the
  sentence's meaning. docs/integrations/forge.md:282,
  docs/tools/forge.md:260, docs/tools/hivectl.md:243,
  docs/web-ui/dashboard.md:457 (and the swarmctl-cli.md generated
  twin of the same category, source left alone for the same reason).
- docs/agent-lifecycle/persistence.md:482 -- 'is not' matched inside
  'is nothing' (the same has-not/has-nothing substring trap noted
  before in this doc's own git history).
- docs/swarm/ca.md:182 -- 'it is' matched inside the already-correct
  'it isn't'.

Per #4128. Remaining errors on main after this: Microsoft.Avoid's 26
hits, already tracked + awaiting a house-style ruling on #4041.

docs/turn-loop/claude-invocation.md

@@ -250,7 +250,7 @@ needs to `chown` a bind mount), once at startup:
 
   **Marker grammar.** `<!-- role:X -->` opens a block; any
   `<!-- /role:X -->` closes the current block. The renderer always uses
-  role `agent`, so it elides blocks with other role tags. Nesting is NOT
+  role `agent`, so it elides blocks with other role tags. Nesting **isn't**
   supported — a stray opener with no closer runs until end of file.
   The renderer tolerates whitespace inside markers (`<!--role:foo-->` parses the
   same as `<!-- role:foo -->`). Content outside any marker is always