feat(persona): add role-based review personas

Add persona system for specialized review roles. Each persona defines:
- A specific review focus (security, architecture, documentation)
- Custom system prompt additions
- Personality/tone adjustments

Built-in personas: security, architect, docs
Custom personas: load from JSON via persona-file flag

Includes workspace validation to prevent path traversal attacks.

Closes #51

go.mod

@@ -2,4 +2,4 @@ module gitea.weiker.me/rodin/review-bot
 
 go 1.26.2
 
-require github.com/goccy/go-yaml v1.19.2
+require gopkg.in/yaml.v3 v3.0.1 // indirect

go.sum

@@ -1,2 +1,3 @@
-github.com/goccy/go-yaml v1.19.2 h1:PmFC1S6h8ljIz6gMRBopkjP1TVT7xuwrButHID66PoM=
-github.com/goccy/go-yaml v1.19.2/go.mod h1:XBurs7gK8ATbW4ZPGKgcbrY1Br56PdM69F7LkFRi1kA=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

review/persona.go

@@ -8,7 +8,7 @@ import (
 	"path/filepath"
 	"strings"
 
-	"github.com/goccy/go-yaml"
+	"gopkg.in/yaml.v3"
 )
 
 //go:embed personas/*.yaml