feat: [FME-17261]: add experiment noun (CRUD)

[apetruccelli]

Description

Note: stacked on top of #257 (still open) — this branch depends on the fme:owners field type introduced there, so the diff below includes #257's commits until it merges.

• Ticket FME-17261 asks for the experiment noun in the FME CLI module with full CRUD support.
• experiment noun, full CRUD: list, get, create, update, delete against v4 (/fme/api/v4/experiments).
  • Experiments are scoped by parent — --parent-type FEATURE_FLAG|AI_CONFIG plus --parent-name/--parent-id — and by --env.
  • create builds the request from --start-at/--end-at/--baseline-treatment/--comparison-treatment/--key-metric/--supporting-metric/--description/--hypothesis, or accepts -f experiment.json as a full alternative.
  • update narrows the get-then-patch body to UpdateExperimentRequest's accepted fields, keeping read-only fields (id, type, parent, environment, timestamps) out of the PATCH — v4 rejects unknown properties.
• fme:metric_refs field type (modules/fme/metric_refs.go): keyMetrics/supportingMetrics read as [{id,name}] but write as plain metric id strings — an asymmetric read/write shape core's built-in set type can't handle since it assumes both shapes match. Normalize strips the display name down to a plain id string; Mutate adds/deletes/dedups on the normalized id list.
• owners is fully mutable, reusing the fme:owners field type already wired onto feature_flag/segment in feat: [FME-17257]: add owners/tags field types, flag_sets, and file (-f) support for feature_flag and segment #257 — no new Go code needed. --add/--del owners.user:<email|id> and owners.group:<identifier> work at both create and update, since flags_builtin: set: true already enables add/del.
• Not supported by v4 (confirmed at the DTO level, not a CLI gap): tags and a client-settable targeting rule are absent from CreateExperimentRequest/UpdateExperimentRequest. The FME web UI's experiment tagging goes through a separate legacy webconsole-bff path, not the public v4 API.

Commands

• harness create experiment <name> --parent-type feature_flag --parent-name my-flag --env <env-id> --start-at 2026-01-01T00:00:00Z --end-at 2026-02-01T00:00:00Z --baseline-treatment off --comparison-treatment on --add owners.user:<email>
• harness create experiment <name> -f experiment.json
• harness list experiment --parent-type FEATURE_FLAG --parent-name my-flag [--env <env-id>] [--status ACTIVE]
• harness get experiment <id>
• harness update experiment <id> --set description="new desc" --add key_metrics.<metric-id> --add owners.user:<email> --del owners.user:<id>
• harness delete experiment <id> --confirm

Testing

• go build ./... and go test ./... pass.
• Unit tests in pkg/specloader/fme_spec_test.go covering all 5 operations: TestFMESpec_ListExperiment, GetExperiment, CreateExperiment, UpdateExperiment, DeleteExperiment, plus TestFMESpec_UpdateExperiment_AddDelOwners.
• Live-verified against qa0: create/list/get/update/delete round trip, owners add/del, key-metric add on update, read-only field exclusion from PATCH.
• Live-verified that --org/--project scope flags and --format json|table (via the shared --format/--json flags) work for list/get experiment, per the ticket's acceptance criteria.

Acceptance Criteria

• All 5 operations implemented (list, get, create, update, delete)
• --org/--project scope flags work
• --format json|table output works for list/get
• Unit tests for each operation

🤖 Generated with Claude Code