[feat] add ACME-based certificate management using go-acme/lego

- Introduced a new `legoManager` for managing per-domain TLS certificates.
- Implemented ACME HTTP-01 challenge handling with a configurable webroot directory.
- Created `NewLegoManagerFromEnv` to initialize ACME settings from environment variables.
- Added `verifyDomainsResolve` to validate domain DNS resolutions.
- Updated `.gitignore` to include ACME cache and webroot directories.
- Updated `go.mod` and `go.sum` with new dependencies, including `go-acme/lego`.

go.mod

@@ -4,7 +4,8 @@ go 1.25.4
 
 require (
 	entgo.io/ent v0.14.5
-	github.com/google/uuid v1.3.0
+	github.com/go-acme/lego/v4 v4.28.1
+	github.com/google/uuid v1.6.0
 	github.com/lib/pq v1.10.9
 	github.com/pion/dtls/v3 v3.0.7
 	golang.org/x/net v0.47.0
@@ -15,9 +16,12 @@ require (
 	github.com/agext/levenshtein v1.2.3 // indirect
 	github.com/apparentlymart/go-textseg/v15 v15.0.0 // indirect
 	github.com/bmatcuk/doublestar v1.3.4 // indirect
+	github.com/cenkalti/backoff/v5 v5.0.3 // indirect
+	github.com/go-jose/go-jose/v4 v4.1.3 // indirect
 	github.com/go-openapi/inflect v0.19.0 // indirect
-	github.com/google/go-cmp v0.6.0 // indirect
+	github.com/google/go-cmp v0.7.0 // indirect
 	github.com/hashicorp/hcl/v2 v2.18.1 // indirect
+	github.com/miekg/dns v1.1.68 // indirect
 	github.com/mitchellh/go-wordwrap v1.0.1 // indirect
 	github.com/pion/logging v0.2.4 // indirect
 	github.com/pion/transport/v3 v3.0.7 // indirect
@@ -26,5 +30,8 @@ require (
 	github.com/zclconf/go-cty-yaml v1.1.0 // indirect
 	golang.org/x/crypto v0.44.0 // indirect
 	golang.org/x/mod v0.29.0 // indirect
+	golang.org/x/sync v0.18.0 // indirect
+	golang.org/x/sys v0.38.0 // indirect
 	golang.org/x/text v0.31.0 // indirect
+	golang.org/x/tools v0.38.0 // indirect
 )