docs(skills): the automation skill's CEL table is the bare-callable public subset (#15524)

`skills/objectstack-automation/SKILL.md` repeated the completeness claim just
corrected one skill over: conditions are bare CEL and "only the stdlib is
callable", pointing at the formula skill for "the full table". Both halves
under-promise — the CEL environment also resolves receiver methods called on a
value, and the catalogue is the advertised bare-callable public subset rather
than everything that resolves.

Corrected in one clause, in this skill's voice: the stdlib is what you may call
bare, the referenced table is `CEL_STDLIB_FUNCTIONS` — the bare-callable public
subset — and receiver methods are called on a value, never bare. The pointer to
objectstack-formula stays; that skill now carries the full statement. No method
or withheld-primitive enumeration is duplicated here.


Claude-Session: https://claude.ai/code/session_019RfFHiRCSs3JXLK4cwcfox

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

Author: claude[bot]

skills/objectstack-automation/SKILL.md

@@ -348,10 +348,12 @@ them right the first time:
    } });
    ```
 
-4. **Conditions are bare CEL — only the stdlib is callable.** `now()`,
+4. **Conditions are bare CEL — the stdlib is what you may call bare.** `now()`,
    `today()`, `daysFromNow(n)`, `daysAgo(n)`, `daysBetween(a, b)`, `isBlank(v)`,
    `coalesce(a, b)`, `abs/round/min/max`, `upper/lower/contains/matches`, plus CEL
-   built-ins (`has`, `size`, `int`, `string`, …) — see **objectstack-formula** for the full table.
+   built-ins (`has`, `size`, `int`, `string`, …) — see **objectstack-formula** for that
+   table: it is `CEL_STDLIB_FUNCTIONS`, the bare-callable public subset, so receiver
+   methods (called on a value, never bare) are not in it.
    An UNKNOWN function (`PRIOR()`, a typo'd name) and a `{…}`-wrapped field ref
    both **fail the build**: a brace is a template, not CEL — write `record.x`,
    not `{record.x}`.