feat(integrations): add omp support (#3107)

* feat(integrations): add omp support

* Update updated_at timestamp

* refactor(integrations): delegate omp build_exec_args to base, register in issue templates

Inherit MarkdownIntegration.build_exec_args so omp picks up shared CLI
contract changes (requires_cli gating, extra-args ordering, --model
handling) automatically; only specialize the --mode json flag.

Also add Oh My Pi / omp to the issue-template agent lists so
test_issue_template_agent_lists_match_runtime_integrations passes.

* fix(integrations): use --print + positional prompt for omp argv

OMP's CLI parser treats `-p`/`--print` as a boolean (one-shot mode)
and consumes the prompt as a positional message; the previous
inherited `-p <prompt>` shape worked by accident only because `-p`
ignores its next token. Build the argv explicitly with flags first
and the prompt as a trailing positional, matching upstream args.ts.

integrations/catalog.json

@@ -1,6 +1,6 @@
 {
   "schema_version": "1.0",
-  "updated_at": "2026-06-22T00:00:00Z",
+  "updated_at": "2026-06-23T00:00:00Z",
   "catalog_url": "https://raw.githubusercontent.com/github/spec-kit/main/integrations/catalog.json",
   "integrations": {
     "claude": {
@@ -255,6 +255,15 @@
       "repository": "https://github.com/github/spec-kit",
       "tags": ["cli"]
     },
+    "omp": {
+      "id": "omp",
+      "name": "Oh My Pi",
+      "version": "1.0.0",
+      "description": "Oh My Pi (omp) terminal coding agent prompt-based integration",
+      "author": "spec-kit-core",
+      "repository": "https://github.com/github/spec-kit",
+      "tags": ["cli"]
+    },
     "iflow": {
       "id": "iflow",
       "name": "iFlow CLI",