migrate: stow → chezmoi

- restructure repo to chezmoi conventions (dot_ prefix, private_dot_ssh/)
- add nvim config (was untracked)
- encrypt restic pass.txt with age
- remove stow artifacts (.stow-local-ignore, stow package dirs)
- update bootstrap.sh to use chezmoi apply
- remove runtime files from tracking (micro buffers, zed backup)

dot_config/micro/settings.json

@@ -0,0 +1,11 @@
+{
+    "autosu": true,
+    "colorscheme": "simple",
+    "mkparents": true,
+    "rmtrailingws": true,
+    "savecursor": true,
+    "saveundo": true,
+    "scrollbar": true,
+    "statusformatl": "$(filename) $(modified)($(line),$(col)) $(opt:filetype) $(opt:fileformat)",
+    "tabstospaces": true
+}