feat(fish): add secrets.d for secret env vars

Add config/fish/secrets.d/ directory pattern to .gitignore while
allowing *.example and README.md through. Add README and example file
documenting the secrets convention. Source secrets.d/*.fish files in
exports.fish so secret environment variables are loaded automatically.

config/fish/secrets.d/README.md

@@ -0,0 +1,72 @@
+# Fish Shell Secrets Directory
+
+This directory contains sensitive environment variables like API tokens and credentials.
+
+## Usage
+
+1. Copy an example file (e.g., `github.fish.example`) to remove the `.example` suffix:
+
+   ```bash
+   cp github.fish.example github.fish
+   ```
+
+2. Edit the file and replace placeholder values with your actual secrets:
+
+   ```bash
+   $EDITOR github.fish
+   ```
+
+3. Reload your fish shell or source the exports:
+
+   ```fish
+   source ~/.config/fish/exports.fish
+   ```
+
+## Adding New Secret Files
+
+Create a new `.fish` file in this directory with your environment variables:
+
+```fish
+# Example: openai.fish
+set -x OPENAI_API_KEY "sk-xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
+```
+
+Common secret patterns:
+
+- `github.fish` - GitHub Personal Access Token (`GITHUB_TOKEN`)
+- `aws.fish` - AWS credentials (`AWS_ACCESS_KEY_ID`, `AWS_SECRET_ACCESS_KEY`)
+- `openai.fish` - OpenAI API key (`OPENAI_API_KEY`)
+- `anthropic.fish` - Anthropic API key (`ANTHROPIC_API_KEY`)
+
+## Security Best Practices
+
+- **Never commit actual secrets** - Only `.example` files are tracked by git
+- **Use specific permissions** - Consider `chmod 600` for secret files
+- **Rotate credentials regularly** - Update tokens when compromised
+- **Use environment-specific files** - Separate dev/staging/prod credentials
+- **Check before committing** - Run `git status` to verify secrets aren't staged
+
+## How It Works
+
+The `exports.fish` file automatically sources all `*.fish` files from this directory:
+
+```fish
+if test -d "$DOTFILES/config/fish/secrets.d"
+    for secret_file in "$DOTFILES/config/fish/secrets.d"/*.fish
+        if test -f "$secret_file"
+            source "$secret_file"
+        end
+    end
+end
+```
+
+Files ending in `.example` are ignored by the loader but tracked by git as templates.
+
+## Backward Compatibility
+
+This directory supplements the existing `exports-secret.fish` pattern. Both methods work:
+
+- **Legacy**: `config/fish/exports-secret.fish` (single file, still supported)
+- **New**: `config/fish/secrets.d/*.fish` (multiple files, recommended)
+
+Use whichever approach fits your workflow best.