rename Fence to Greywall as GreyHaven sandboxing component

Rebrand the project from Fence to Greywall, the sandboxing layer of the
GreyHaven platform. This updates:

- Go module path to gitea.app.monadical.io/monadical/greywall
- Binary name, CLI help text, and all usage examples
- Config paths (~/.config/greywall/greywall.json), env vars (GREYWALL_*)
- Log prefixes ([greywall:*]), temp file prefixes (greywall-*)
- All documentation, scripts, CI workflows, and example files
- README rewritten with GreyHaven branding and Fence attribution

Directory/file renames: cmd/fence → cmd/greywall, pkg/fence → pkg/greywall,
docs/why-fence.md → docs/why-greywall.md, example JSON files, and banner.

docs/quickstart.md

@@ -5,16 +5,16 @@
 ### From Source (recommended for now)
 
 ```bash
-git clone https://github.com/Use-Tusk/fence
-cd fence
-go build -o fence ./cmd/fence
-sudo mv fence /usr/local/bin/
+git clone https://gitea.app.monadical.io/monadical/greywall
+cd greywall
+go build -o greywall ./cmd/greywall
+sudo mv greywall /usr/local/bin/
 ```
 
 ### Using Go Install
 
 ```bash
-go install github.com/Use-Tusk/fence/cmd/fence@latest
+go install gitea.app.monadical.io/monadical/greywall/cmd/greywall@latest
 ```
 
 ### Linux Dependencies
@@ -32,30 +32,30 @@ sudo dnf install bubblewrap socat
 sudo pacman -S bubblewrap socat
 ```
 
-### Do I need sudo to run fence?
+### Do I need sudo to run greywall?
 
-No, for most Linux systems. Fence works without root privileges because:
+No, for most Linux systems. Greywall works without root privileges because:
 
 - Package-manager-installed `bubblewrap` is typically already setuid
-- Fence detects available capabilities and adapts automatically
+- Greywall detects available capabilities and adapts automatically
 
-If some features aren't available (like network namespaces in Docker/CI), fence falls back gracefully - you'll still get filesystem isolation, command blocking, and proxy-based network filtering.
+If some features aren't available (like network namespaces in Docker/CI), greywall falls back gracefully - you'll still get filesystem isolation, command blocking, and proxy-based network filtering.
 
-Run `fence --linux-features` to see what's available in your environment.
+Run `greywall --linux-features` to see what's available in your environment.
 
 ## Verify Installation
 
 ```bash
-fence --version
+greywall --version
 ```
 
 ## Your First Sandboxed Command
 
-By default, fence blocks all network access:
+By default, greywall blocks all network access:
 
 ```bash
 # This will fail - network is blocked
-fence curl https://example.com
+greywall curl https://example.com
 ```
 
 You should see something like:
@@ -66,7 +66,7 @@ curl: (56) CONNECT tunnel failed, response 403
 
 ## Allow Specific Domains
 
-Create a config file at `~/.config/fence/fence.json` (or `~/Library/Application Support/fence/fence.json` on macOS):
+Create a config file at `~/.config/greywall/greywall.json` (or `~/Library/Application Support/greywall/greywall.json` on macOS):
 
 ```json
 {
@@ -79,7 +79,7 @@ Create a config file at `~/.config/fence/fence.json` (or `~/Library/Application
 Now try again:
 
 ```bash
-fence curl https://example.com
+greywall curl https://example.com
 ```
 
 This time it succeeds!
@@ -89,7 +89,7 @@ This time it succeeds!
 Use `-d` to see what's happening under the hood:
 
 ```bash
-fence -d curl https://example.com
+greywall -d curl https://example.com
 ```
 
 This shows:
@@ -103,7 +103,7 @@ This shows:
 Use `-m` to see only violations and blocked requests:
 
 ```bash
-fence -m npm install
+greywall -m npm install
 ```
 
 This is useful for:
@@ -117,7 +117,7 @@ This is useful for:
 Use `-c` to run compound commands:
 
 ```bash
-fence -c "echo hello && ls -la"
+greywall -c "echo hello && ls -la"
 ```
 
 ## Expose Ports for Servers
@@ -125,14 +125,14 @@ fence -c "echo hello && ls -la"
 If you're running a server that needs to accept connections:
 
 ```bash
-fence -p 3000 -c "npm run dev"
+greywall -p 3000 -c "npm run dev"
 ```
 
 This allows external connections to port 3000 while keeping outbound network restricted.
 
 ## Next steps
 
-- Read **[Why Fence](why-fence.md)** to understand when fence is a good fit (and when it isn't).
+- Read **[Why Greywall](why-greywall.md)** to understand when greywall is a good fit (and when it isn't).
 - Learn the mental model in **[Concepts](concepts.md)**.
 - Use **[Troubleshooting](troubleshooting.md)** if something is blocked unexpectedly.
 - Start from copy/paste configs in **[`docs/templates/`](templates/README.md)**.