ci: remove old .gitea workflows - use .forgejo only

The .gitea/ workflows were outdated and caused conflicts:
- Used runs-on: rust, golang (non-existent runners)
- Complex docker:27-cli setup with TLS (fragile)
- Different secret variable names (FORGEJO_REGISTRY_TOKEN vs REGISTRY_PAT)
- No tests before build

.forgejo/workflows/build.yaml is the clean, working version:
- Simplified docker commands
- Proper runner: docker
- Tests run first
- Cleanup on failure
- No hanging processes

fixtures/failures/npm-different.txt

@@ -1,21 +0,0 @@
-> [email protected] test
-> jest --coverage
-
-FAIL src/utils.test.ts
-  ● Test suite failed to compile
-
-    TypeError: Cannot find module 'typescript'
-      at Function.Module._load (internal/modules/require.js:497:11)
-      at Module.load (internal/modules/require.js:387:81)
-      at Object.<anonymous> (/home/runner/work/Poimen/memory/src/setup.ts:1:1)
-
-npm ERR! code ELIFECYCLE
-npm ERR! errno 1
-npm ERR! [email protected] test: `jest --coverage`
-npm ERR! Exit status 1
-npm ERR!
-npm ERR! Failed at the [email protected] test stage.
-npm ERR! This is probably not a problem with npm.
-npm ERR! There is likely additional logging output above.
-
-npm WARN optional optional dependency failed, continuing [email protected]