Add support for ECDSA P-384 (#685)

## Motivation and Context

See
https://github.com/modelcontextprotocol/registry/issues/482#issuecomment-3436993157
for full details.

This adds ECDSA P-384 (a popular NIST approved curve) in addition to
Ed25519.

## How Has This Been Tested?

I have tested with a local deployment against `mcp.joelverhagen.com`.
Also, I have added significant tests.

## Breaking Changes

None. (hopefully)

## Types of changes
<!-- What types of changes does your code introduce? Put an `x` in all
the boxes that apply: -->
- [ ] Bug fix (non-breaking change which fixes an issue)
- [x] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)
- [x] Documentation update

## Checklist
<!-- Go over all the following points, and put an `x` in all the boxes
that apply. -->
- [x] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [x] My code follows the repository's style guidelines
- [x] New and existing tests pass locally
- [x] I have added appropriate error handling
- [x] I have added or updated documentation as needed

## Additional context
<!-- Add any other context, implementation notes, or design decisions
-->

@domdomegg and I spoke a bit about this on Discord:
https://discord.com/channels/1358869848138059966/1369487942862504016/1423710918180606052

---------

Co-authored-by: adam jones <domdomegg+git@gmail.com>

docs/guides/publishing/publish-server.md

@@ -468,6 +468,8 @@ echo "yourcompany.com. IN TXT \"v=MCPv1; k=ed25519; p=$(openssl pkey -in key.pem
 mcp-publisher login dns --domain yourcompany.com --private-key $(openssl pkey -in key.pem -noout -text | grep -A3 "priv:" | tail -n +2 | tr -d ' :\n')
 ```
 
+The ECDSA P-384 crypto algorithm is also supported, along with HTTP-based authenication. See the [publisher CLI commands reference](../../reference/cli/commands.md) for more details.
+
 ## Step 5: Publish Your Server
 
 With authentication complete, publish your server:

docs/reference/cli/commands.md

@@ -80,9 +80,9 @@ mcp-publisher login dns --domain=example.com --private-key=HEX_KEY [--registry=U
 ```
 - Verifies domain ownership via DNS TXT record
 - Grants access to `com.example.*` namespaces
-- Requires Ed25519 private key (64-character hex)
+- Requires Ed25519 private key (64-character hex) or ECDSA P-384 private key (96-character hex)
 
-**Setup:**
+**Setup:** (for Ed25519, recommended)
 ```bash
 # Generate keypair
 openssl genpkey -algorithm Ed25519 -out key.pem
@@ -97,15 +97,30 @@ openssl pkey -in key.pem -pubout -outform DER | tail -c 32 | base64
 openssl pkey -in key.pem -noout -text | grep -A3 "priv:" | tail -n +2 | tr -d ' :\n'
 ```
 
+**Setup:** (for ECDSA P-384)
+```bash
+# Generate keypair
+openssl genpkey -algorithm EC -pkeyopt ec_paramgen_curve:secp384r1 -out key.pem
+
+# Get public key for DNS record
+openssl ec -in key.pem -text -noout -conv_form compressed | grep -A4 "pub:" | tail -n +2 | tr -d ' :\n' | xxd -r -p | base64
+
+# Add DNS TXT record:
+# example.com. IN TXT "v=MCPv1; k=ecdsap384; p=PUBLIC_KEY"
+
+# Extract private key for login
+openssl ec -in <pem path> -noout -text | grep -A4 "priv:" | tail -n +2 | tr -d ' :\n'
+```
+
 #### HTTP Verification
 ```bash
 mcp-publisher login http --domain=example.com --private-key=HEX_KEY [--registry=URL]
 ```
 - Verifies domain ownership via HTTPS endpoint  
 - Grants access to `com.example.*` namespaces
-- Requires Ed25519 private key (64-character hex)
+- Requires Ed25519 private key (64-character hex) or ECDSA P-384 private key (96-character hex)
 
-**Setup:**
+**Setup:** (for Ed25519, recommended)
 ```bash
 # Generate keypair (same as DNS)
 openssl genpkey -algorithm Ed25519 -out key.pem
@@ -115,6 +130,16 @@ openssl genpkey -algorithm Ed25519 -out key.pem
 # Content: v=MCPv1; k=ed25519; p=PUBLIC_KEY
 ```
 
+**Setup:** (for ECDSA P-384)
+```bash
+# Generate keypair (same as DNS)
+openssl genpkey -algorithm EC -pkeyopt ec_paramgen_curve:secp384r1 -out key.pem
+
+# Host public key at:
+# https://example.com/.well-known/mcp-registry-auth
+# Content: v=MCPv1; k=ecdsap384; p=PUBLIC_KEY
+```
+
 #### Anonymous (Testing)
 ```bash
 mcp-publisher login none [--registry=URL]