feat(functions): add open-url and repo-open browser helpers

Extract the browser-detection and launch logic out of config-help into a
reusable open-url function, then build repo-open on top of it to open the
current repo's origin remote in a browser.

- open-url: resolve the best graphical browser (fish_help_browser -> BROWSER
  -> xdg-mime https handler -> known binaries -> xdg-open) and launch it
  backgrounded. Silent by default; -v/--verbose reports the browser, -s/--silent
  is accepted explicitly. Browser console chatter is discarded.
- repo-open: normalize the origin URL from HTTPS and SSH/scp forms, deep-link
  to the current branch (falling back to the remote default) and sub-directory.
  Provider layout resolved via git config browse.provider, hostname heuristic
  (github/gitlab/gitea/bitbucket, codeberg->gitea), then github default.
  -p/--print emits the URL, -r/--root ignores the sub-directory.
- config-help: replace the inlined browser block with an open-url call.
- abbr: add open-repo and url-open abbreviations that expand to the canonical
  command names on space/enter.
- docs: document both functions in the SSoT (fish-config.md + index) and add a
  repo-open row to the README doc-browsing table.

docs/fish-config.index

@@ -157,6 +157,10 @@ spark=### spark
 yt-dlp=### yt-dlp
 miscfns=## 5.14 Miscellaneous
 config-help=### config-help
+open-url=### open-url
+url-open=### open-url
+repo-open=### repo-open
+open-repo=### repo-open
 config-update=### config-update
 config-settings=### config-settings
 config-toggle=### config-settings

docs/fish-config.md

@@ -1339,6 +1339,69 @@ Add -i (interactive confirmation) to destructive commands:
 
     Also available as: help config [SECTION] [FLAGS]
 
+### open-url
+
+    Synopsis:  open-url [-s|--silent] [-v|--verbose] <url>
+               open-url -h | --help
+
+    Opens a URL or file:// URI in the best available graphical web browser,
+    backgrounded so it never blocks the terminal. Resolves a real browser
+    binary rather than deferring to xdg-open, whose MIME dispatch can hand
+    local text/html files to non-browser apps (e.g. ebook readers).
+
+    Silent by default: prints nothing on success (errors always go to
+    stderr). Pass --verbose / -v to report which browser is launched;
+    --silent / -s is accepted for explicitness.
+
+    Resolution order:
+      1. $fish_help_browser  (explicit override)
+      2. $BROWSER            (validated; errors if not a command)
+      3. xdg-mime default handler for x-scheme-handler/https
+      4. First known browser binary found in a built-in list
+      5. xdg-open            (last resort)
+
+    open-url https://git.rootiest.dev/rootiest/fish-config
+    open-url "file://$HOME/.config/fish/docs/html/index.html"
+
+    Used internally by config-help --html.
+
+    Typo abbreviation: url-open (expands to open-url on space/enter).
+
+### repo-open
+
+    Synopsis:  repo-open [-p|--print] [-r|--root]
+               repo-open -h | --help
+
+    Opens the web page for the current repository's `origin` remote in a
+    browser (via open-url). Deep-links to the current branch when it exists
+    on the remote — falling back to the remote's default branch (main/master)
+    otherwise — and to the current sub-directory when run below the repo root.
+
+    The remote URL is normalized from HTTPS and SSH/scp forms
+    (git@host:owner/repo.git, ssh://…, https://…). The web path layout is
+    provider-specific; the provider is resolved in order:
+
+      1. git config browse.provider   (per-repo or --global override)
+      2. Hostname heuristic           (github / gitlab / gitea / bitbucket;
+                                        codeberg → gitea)
+      3. Default: github-style layout
+
+    Self-hosted hosts the heuristic can't classify (a Gitea/GitLab instance
+    on a custom domain) need a one-time override:
+
+      git config browse.provider gitea
+
+    Flags:
+      --print / -p   Print the resolved URL instead of opening it.
+      --root  / -r   Ignore the current sub-directory; link to the repo root.
+      --help  / -h   Show usage.
+
+    repo-open
+    repo-open --print
+    repo-open --root
+
+    Typo abbreviation: open-repo (expands to repo-open on space/enter).
+
 ### config-update
 
     Synopsis:  config-update [-h] [-n] [-f]