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The .gitea/ workflows were outdated and caused conflicts: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

@@ -1,23 +0,0 @@
-> [email protected] build
-> cargo build --release
-
-Compiling mem-cli v0.1.0 (/home/ubuntu/workspace/Poimen/memory/crates/mem-cli)
-error: unresolved import `mem_core`
- --> crates/mem-cli/src/main.rs:15:5
-  |
-15 | use mem_core::{Record, Provenance, Role};
-   |     ^^^^^^^^ could not find `mem_core` in `extern prelude`
-   |
-   = note: consider adding `extern crate mem_core` to use the crate
-
-error: could not compile `mem-cli` due to previous error
-
-npm ERR! code ELIFECYCLE
-npm ERR! errno 1
-npm ERR! [email protected] build: `cargo build --release`
-npm ERR! Exit status 1
-npm ERR! 
-npm ERR! Failed at the [email protected] build stage.
-npm ERR! Make sure you have the latest version of node.js and npm installed.
-
-npm WARN optional optional dependency failed, continuing [email protected]