fix: Bicep module ref path — strip bicep/ prefix, lookup by ref_path

Two bugs fixed in BicepModuleCatalog:

1. as_completion_items() generated 'br/modules:bicep/modules/appservice:...'
   but bicepconfig modulePath='bicep' means Bicep prepends 'bicep/' automatically.
   Fix: store ref_path = path.removeprefix('bicep/') and use it in insertText.
   Correct output: 'br/modules:modules/appservice:2.3.x'

2. version/param lookups used get_module_by_name() which only matches the last
   path segment ('appservice'). New-style refs capture 'modules/appservice' from
   the regex, so lookup returned empty. Fix: add get_module_by_ref() that matches
   both ref_path and bare name.

Also fixes _iac_param_map to strip path prefix so IAC source descriptions
still enrich completions for 'modules/appservice' refs.

All 63 tests pass.

tests/test_proxy.py

@@ -31,9 +31,11 @@ def _completion_response(items: list) -> dict:
 
 def _make_module(name, versions=None, schema=None):
     versions = versions or ["1.0.0", "latest"]
+    path = f"bicep/modules/{name}"
     return {
         "name": name,
-        "path": f"bicep/modules/{name}",
+        "path": path,
+        "ref_path": f"modules/{name}",  # what appears after 'br/modules:' in bicep files
         "versions": versions,
         "latest": versions[-1],
         "registry": "iactemplatereg.azurecr.io",