refactor(forge): remove %l eol specifier, add auto_close config, fix icons

Problem: `%l` was dead code after inline overlays replaced EOL
rendering. Auto-close was always on with no opt-out. Forge icon
defaults were empty strings.

Solution: remove `%l` from the eol format parser and renderer. Add
`forge.auto_close` (default `false`) to gate state-pull. Set nerd
font icons: `` (GitHub), `` (GitLab), `` (Codeberg). Keep
conceal active in insert mode via `concealcursor = 'nic'`.

lua/pending/config.lua

@@ -40,6 +40,7 @@
 ---@field instances? string[]
 
 ---@class pending.ForgeConfig
+---@field auto_close? boolean
 ---@field github? pending.ForgeInstanceConfig
 ---@field gitlab? pending.ForgeInstanceConfig
 ---@field codeberg? pending.ForgeInstanceConfig
@@ -154,18 +155,19 @@ local defaults = {
   },
   sync = {},
   forge = {
+    auto_close = false,
     github = {
-      icon = '',
+      icon = '',
       issue_format = '%i %o/%r#%n',
       instances = {},
     },
     gitlab = {
-      icon = '',
+      icon = '',
       issue_format = '%i %o/%r#%n',
       instances = {},
     },
     codeberg = {
-      icon = '',
+      icon = '',
       issue_format = '%i %o/%r#%n',
       instances = {},
     },