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The .gitea/ workflows were outdated and caused conflicts: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/cargo-run-a.txt

@@ -1,12 +0,0 @@
-   Compiling mem-cli v0.1.0 (/home/runner/work/Poimen/memory/crates/mem-cli)
-error[E0599]: no method named `unwrap_or` found for struct `Result` in this scope
-   --> crates/mem-cli/src/main.rs:456:78
-    |
-456 |         let database_url = database_url.unwrap_or_else(|| std::env::var("DATABASE_URL").unwrap_or_else(|_| "postgresql://app:poimen@localhost:5432/memory".to_string()));
-    |                                                                                          ^^^^^^^^^^^^^^^ method not found in `Result<String, VarError>`
-    |
-   = note: the following candidate methods were found:
-     <alloc::result::Result<T, E> as core::ops::try::Try>::into_ok
-     <alloc::result::Result<T, E> as core::ops::try::Try>::into_err
-
-error: could not compile `mem-cli` due to 1 previous error