docs(workflows): verify the reference model against the resolver; fix one imprecision

Checked every claim in the new 'One syntax, named sources' section against
apps/sim/executor/variables: resolver chain order is Loop -> Parallel ->
WorkflowVariables -> Env -> Block (matches the table); 'variable'/'loop'/
'parallel' are literal prefixes (REFERENCE.PREFIX); block names normalize via
toLowerCase + strip spaces; an unmatched reference is genuinely left in place
(resolver returns undefined -> the replacer emits the raw match). One claim
tightened: {{KEY}} is a different syntax and can never collide with
angle-bracket references, so the precedence sentence now scopes collisions to
the angle-bracket sources with a concrete example (a block named 'variable').

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: ouiliame

apps/docs/content/docs/en/workflows/variables.mdx

@@ -21,7 +21,7 @@ Everything in angle brackets is the same mechanism: `<name.path>` reads a value
 | `{{KEY}}` | An environment variable | `{{OPENAI_API_KEY}}` |
 | `<blockname.field>` | A block's output — a connection tag, not a variable | `<agent.content>` |
 
-The table is in resolution order: when a reference could match more than one thing, loop and parallel context win, then workflow variables, then environment variables, then block outputs. If nothing matches, the raw reference is left in place unsubstituted, which usually breaks the block that reads it — so give variables and blocks distinct names.
+The table is in resolution order: when an angle-bracket reference could match more than one source — say a block named `variable` — loop and parallel context win, then workflow variables, then block outputs. (`{{KEY}}` can't collide; it's a different syntax.) If nothing matches, the raw reference is left in place unsubstituted, which usually breaks the block that reads it — so give variables and blocks distinct names.
 
 Type `<` in any block text field to open the picker and browse everything you can reference.