Strict2 rejection specs point to self['...'] in error message and hints

All 7 strict2 bare-bracket rejection specs now:
- Check error message contains 'self' (liquid-ruby's error says
  'Use self[\'...\'] instead')
- Hints point to self['...'] as the replacement syntax

Full error-mode matrix verified (Ruby liquid + JSON-RPC):
  Lax:     15 failures (strict2 specs fail — lax allows bare brackets)
  Strict:  101 failures (lax recovery specs fail — strict rejects)
  Strict2: 188 failures (lax+strict specs fail — strict2 rejects)
Both adapters match exactly: 15/101/188 failures in each mode.

Declared-mode suite: 0 failures on both adapters.
7 verifiers pass. 92 unit tests pass.

Author: tobi

specs/liquid_ruby/bare_bracket_self.yml

@@ -14,26 +14,31 @@
   errors:
     parse_error:
       - "Bare bracket access is not allowed"
+      - "self"
   hint: |
     In strict2 mode, bare-bracket access like ['product'] is rejected.
-    The parser should raise a SyntaxError when it encounters an open
-    square bracket at the start of an expression.
+    The error message points to self['...'] as the replacement.
+    Use self['product'] instead — it resolves the variable through the
+    normal scope chain.
 
 - name: strict2_rejects_bare_bracket_double_quoted
   template: '{{ ["product"] }}'
   error_mode: strict2
   errors:
     parse_error:
       - "Bare bracket access is not allowed"
+      - "self"
   hint: |
     Double-quoted bare-bracket access is also rejected in strict2 mode.
+    Use self["product"] instead.
 
 - name: strict2_rejects_bare_bracket_dynamic_lookup
   template: "{{ [key] }}"
   error_mode: strict2
   errors:
     parse_error:
       - "Bare bracket access is not allowed"
+      - "self"
   hint: |
     Dynamic variable lookup via bare brackets is rejected in strict2 mode.
     Use self[key] instead.
@@ -44,35 +49,43 @@
   errors:
     parse_error:
       - "Bare bracket access is not allowed"
+      - "self"
   hint: |
     Bare brackets in for loop collections are rejected in strict2 mode.
+    Use self['collection'] instead.
 
 - name: strict2_rejects_bare_bracket_in_if
   template: "{% if ['product'] == true %}hello{% endif %}"
   error_mode: strict2
   errors:
     parse_error:
       - "Bare bracket access is not allowed"
+      - "self"
   hint: |
     Bare brackets in if conditions are rejected in strict2 mode.
+    Use self['product'] instead.
 
 - name: strict2_rejects_bare_bracket_in_case
   template: "{% case ['product'] %}{% when 'a' %}hello{% endcase %}"
   error_mode: strict2
   errors:
     parse_error:
       - "Bare bracket access is not allowed"
+      - "self"
   hint: |
     Bare brackets in case expressions are rejected in strict2 mode.
+    Use self['product'] instead.
 
 - name: strict2_rejects_bare_bracket_in_assign
   template: "{% assign x = ['product'] %}"
   error_mode: strict2
   errors:
     parse_error:
       - "Bare bracket access is not allowed"
+      - "self"
   hint: |
     Bare brackets in assign values are rejected in strict2 mode.
+    Use self['product'] instead.
 
 - name: strict2_accepts_qualified_bracket_access
   template: "{{ product['title'] }}"