Update declarative agent templates to schema/version v1.8

[Copilot]

The declarative agent scaffolding templates were still pinned to manifest schema v1.7. This updates template outputs to v1.8 consistently across all DA template families, with no behavioral/template-shape changes beyond versioning.

• Scope: declarative agent template manifests

  • Updated all DA manifest template files that emit declarativeAgent.json / repairDeclarativeAgent.json.
  • Applied uniformly across:
    • templates/vsc/** (common/js/ts)
    • templates/vs/** (csharp)
    • templates/v4/create/da/**

• What changed

  • Bumped schema URL from .../declarative-agent/v1.7/schema.json to .../declarative-agent/v1.8/schema.json.
  • Bumped manifest version field from "v1.7" to "v1.8".

• Representative diff

{
  "$schema": "https://developer.microsoft.com/json-schemas/copilot/declarative-agent/v1.8/schema.json",
  "version": "v1.8"
}

• Fixes Update Declarative Agent Manifest Version to v1.8 in each template #16425

[HuihuiWu-Microsoft]

@copilot help me summarize why agent skill feature still works while agent_skill is removed from v1.8 schema when the agent skill template is marked at v1.8 and v1.9 manifest

[Copilot]

@copilot help me summarize why agent skill feature still works while agent_skill is removed from v1.8 schema when the agent skill template is marked at v1.8 and v1.9 manifest

It still works for two reasons:

1. In this repo, DA schema v1.8 still includes agent_skills (packages/manifest/src/json-schemas/copilot/declarative-agent/v1.8/schema.json), so the skill template at v1.8 is valid.

2. Runtime packaging has compatibility paths:

• DA path reads both agent_skills and x-agent_skills when zipping app package (packages/fx-core/src/component/driver/teamsApp/createAppPackage.ts).
• Add-skill flow also writes top-level Teams manifest agentSkills (packages/fx-core/src/core/FxCore.ts), and packaging processes that as well.

So even if a newer DA schema version removes agent_skills, skill packaging can still work via the Teams manifest agentSkills path/back-compat handling.