feat(agents): resolve Foundry project from endpoint so deploy runs without provision

[huimiu]

What

Stacks on #8629. Adds endpoint-based Foundry project resolution so azd deploy can target an existing Foundry project via endpoint: without azd provision (design spec #8590 §1.4).

Today the microsoft.foundry deploy path resolves the target resource through the shared GetTargetResource -> ensureFoundryProject, which hard-requires AZURE_AI_PROJECT_ID (an ARM id normally written by provision). With only endpoint: set, deploy fails before any data-plane call. This unblocks the minimal end-to-end demo against an existing project.

Changes

• internal/project/foundry_project_resolve.go (new):
  • parseFoundryEndpoint - parse account/project from https://<account>.services.ai.azure.com/api/projects/<project>.
  • resolveFoundryProjectIDFromEndpoint - list Foundry projects in the subscription, match account+project, return the ARM resource id.
  • FoundryServiceTargetProvider.resolveProjectFromEndpoint - when AZURE_AI_PROJECT_ID is absent and an endpoint is available (service endpoint: with ${VAR} expansion, or FOUNDRY_PROJECT_ENDPOINT), resolve and persist AZURE_AI_PROJECT_ID.
• internal/project/service_target_foundry.go - Initialize calls resolveProjectFromEndpoint after auth setup.
• internal/project/foundry_project_resolve_test.go (new) - table-driven parseFoundryEndpoint coverage.

Provisioned projects are unaffected: resolution is skipped when AZURE_AI_PROJECT_ID already exists.

Out of scope (follow-ups toward the minimal demo)

init rework (one-file azure.yaml), data-plane reconcile (deployments/connections/...), built-in Bicep provision, $ref wiring, multi-agent fan-out.

Testing

Extension module: go build ./..., go vet, go test ./internal/project/..., golangci-lint run (0 issues), gofmt, cspell - all clean.

[huimiu]

Folded into #8629 (combined PR: service target + endpoint resolution, targeting huimiu/foundry-azure-yaml). Auto-marked merged because this commit landed on the shared base branch; tracking continues in #8629.