Add Daml code-snippet modules for Canton Network documentation

[8bitpal]

Summary

15 compilable Daml modules wrapping 29 code snippets from docs.canton.network. These ensure that Daml code examples shown in the documentation are compilation-checked by the existing daml_test infrastructure.

What's included

• 15 .daml modules in sdk/docs/source/sdk/docs-canton-network/code-snippets/
• 1 Bazel target (docs-canton-network-daml-test) added to sdk/docs/BUILD.bazel
• 1 daml.yaml for local validation with dpm build

Module list

Module	Snippets	Source pages
DocsCN_AppdevDeepDivesCompositionMultiParty	1	Multi-party workflow composition
DocsCN_AppdevDeepDivesPrivacyModel	1	Privacy model deep dive
DocsCN_AppdevModulesM1MentalModels	1	Canton mental models
DocsCN_AppdevModulesM2MigrationChecklist	1	Migration checklist
DocsCN_AppdevModulesM2MultiPartyWorkflows	3	Multi-party workflow patterns
DocsCN_AppdevModulesM2SmartContractParadigm	2	Smart contract paradigm
DocsCN_AppdevModulesM3DesignPatterns	1	Composition and design patterns
DocsCN_AppdevModulesM3LanguageFundamentals	7	Language fundamentals
DocsCN_AppdevModulesM4BackendDev	1	Backend development (LicenseComment template)
DocsCN_AppdevModulesM7Performance	2	Performance best practices
DocsCN_AppdevReferenceDamlLanguageReference	2	Daml language reference
DocsCN_AppdevTroubleshootingGuideDevelopmentIssues	1	Troubleshooting
DocsCN_OverviewLearnLedgerModel	2	Ledger model overview
DocsCN_OverviewLearnPrivacyModel	1	Privacy model overview
DocsCN_SdksToolsCliToolsDamlScript	3	Daml Script CLI reference

How it works

The Bazel target uses the same pattern as existing doc snippet tests:

daml_test(
    name = "docs-canton-network-daml-test",
    timeout = "long",
    srcs = glob(["source/sdk/docs-canton-network/code-snippets/**/*.daml"]),
    deps = ["//daml-script/daml:daml-script.dar"],
)

New .daml files added to code-snippets/ are auto-discovered by the glob.

Validation

All modules compile successfully with dpm build (SDK 3.4.10). Fragment snippets (choice bodies, expressions) are included as comments within wrapper templates for documentation traceability.