sync working, files from desktop added, next files from laptop and update index.md

git_basics.md

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+# Git Basics
+
+## git push — remote vs branch syntax
+
+**Problem:** `git push -u main` throws:
+fatal: 'main' does not appear to be a git repository
+fatal: Could not read from remote repository.
+
+**Diagnosis:** Git expected a remote name but got a branch name.
+
+**Fix:**
+git push -u origin main
+
+**Key insight:** The syntax is always remote first, branch second.
+`origin` = where to push (the remote repository)
+`main` = which branch to push
+`-u` = sets origin/main as the default tracking branch,
+so future pushes only need `git push`

ssh_keys_and_agent.md

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+# SSH Keys & Agent
+
+## SSH Keypair — per device setup
+
+**Problem:** No SSH key exists on the device yet.
+**Fix:**
+ssh-keygen -t ed25519 -f ~/.ssh/id_ed25519
+**Key insight:** One keypair per device — not per service. Private key never leaves the machine. Public key goes to the server/Forgejo/GitHub.
+
+---
+
+## ~/.ssh/config — Host entry with Port
+
+**Problem:** Forgejo runs on a non-standard port (e.g. 2222) — SSH doesn't know that by default.
+**Fix:**
+Host git.bujour.de
+    HostName git.bujour.de
+    User git
+    Port 2222
+    IdentityFile ~/.ssh/id_ed25519
+**Key insight:** Port gets its own line in the config — not appended to HostName.
+
+---
+
+## ssh-agent + ssh-add
+
+**Problem:** SSH asks for passphrase on every push/pull.
+**Symptom:** `Could not open a connection to your authentication agent.`
+**Diagnosis:** Agent isn't running yet.
+**Fix:**
+eval "$(ssh-agent -s)"
+ssh-add ~/.ssh/id_ed25519
+**Key insight:** `ssh-agent` must be started first with `eval "$(ssh-agent -s)"` before `ssh-add` works. Agent only lives for the current session — needs autostart via `.bashrc` or `.profile` (TODO).
+
+---
+
+## Forgejo SSH authentication — success message
+
+**Problem/Confusion:** After `ssh -T git@git.bujour.de` the response says "Forgejo does not provide shell access" — looks like an error.
+**Key insight:** This is the success message. Forgejo (like GitHub) intentionally blocks interactive shell sessions. "Successfully authenticated" in the same message confirms it worked.