feat: add personal skill storage, API, and SDK (#25363)

> Mux updated this PR on behalf of Mike.

## Stack Context

This PR is the storage, permissions, API, and SDK layer for experimental
personal skills. #25362 has landed on `main`, so this branch is
restacked directly on `main`.

Stack order:
1. #25363 storage, permissions, API, and SDK
2. #25365 API test coverage
3. #25366 chattool and chatd integration
4. #25066 settings UI and docs
5. #25386 personal skills slash menu

## What?

Adds the `user_skills` database table, generated queries, RBAC resources
and scopes, audit resource handling, experimental user-scoped CRUD
endpoints, SDK types, and generated API/site types.

Follow-up review and restack fixes:
- Enforce a bounded personal skill description in parser and database
constraints.
- Return `403 Forbidden` for unauthorized create and update attempts.
- Return explicit conflict responses when soft-deleted users are
targeted.
- Keep user admins out of personal skills, while site owners can read
and delete but not create or update.
- Document trigger-raised constraint names and keep schema constants
covered by tests.
- Reuse `UserSkillMetadata` in the full `UserSkill` SDK response type.
- Generate user skill IDs in Go instead of relying on a database
default.
- Rebase on latest `main` and renumber the user skills migration to
`000502_user_skills`.

## Why?

Personal skills need durable user-owned storage with owner
authorization, limited site-owner moderation, and a hidden API surface
before chatd can consume them.

## Validation

- `make gen`
- `go test ./coderd/database -run '^TestUserSkillSchemaConstants$'
-count=1`
- `go test ./coderd/database/dbauthz -run
'^TestMethodTestSuite/TestUserSkills$' -count=1`
- `go test ./coderd -run '^TestPatchUserSkill$' -count=1`
- `go test ./codersdk ./coderd/database/db2sdk`
- `make lint`
- pre-commit hook on `97fd58108d`

coderd/database/models.go

@@ -312,6 +312,11 @@ const (
 	ApiKeyScopeAiProviderRead                      APIKeyScope = "ai_provider:read"
 	ApiKeyScopeAiProviderUpdate                    APIKeyScope = "ai_provider:update"
 	ApiKeyScopeChatShare                           APIKeyScope = "chat:share"
+	ApiKeyScopeUserSkillCreate                     APIKeyScope = "user_skill:create"
+	ApiKeyScopeUserSkillRead                       APIKeyScope = "user_skill:read"
+	ApiKeyScopeUserSkillUpdate                     APIKeyScope = "user_skill:update"
+	ApiKeyScopeUserSkillDelete                     APIKeyScope = "user_skill:delete"
+	ApiKeyScopeUserSkill                           APIKeyScope = "user_skill:*"
 )
 
 func (e *APIKeyScope) Scan(src interface{}) error {
@@ -567,7 +572,12 @@ func (e APIKeyScope) Valid() bool {
 		ApiKeyScopeAiProviderDelete,
 		ApiKeyScopeAiProviderRead,
 		ApiKeyScopeAiProviderUpdate,
-		ApiKeyScopeChatShare:
+		ApiKeyScopeChatShare,
+		ApiKeyScopeUserSkillCreate,
+		ApiKeyScopeUserSkillRead,
+		ApiKeyScopeUserSkillUpdate,
+		ApiKeyScopeUserSkillDelete,
+		ApiKeyScopeUserSkill:
 		return true
 	}
 	return false
@@ -792,6 +802,11 @@ func AllAPIKeyScopeValues() []APIKeyScope {
 		ApiKeyScopeAiProviderRead,
 		ApiKeyScopeAiProviderUpdate,
 		ApiKeyScopeChatShare,
+		ApiKeyScopeUserSkillCreate,
+		ApiKeyScopeUserSkillRead,
+		ApiKeyScopeUserSkillUpdate,
+		ApiKeyScopeUserSkillDelete,
+		ApiKeyScopeUserSkill,
 	}
 }
 
@@ -3322,6 +3337,7 @@ const (
 	ResourceTypeAiProvider                  ResourceType = "ai_provider"
 	ResourceTypeAiProviderKey               ResourceType = "ai_provider_key"
 	ResourceTypeGroupAiBudget               ResourceType = "group_ai_budget"
+	ResourceTypeUserSkill                   ResourceType = "user_skill"
 )
 
 func (e *ResourceType) Scan(src interface{}) error {
@@ -3392,7 +3408,8 @@ func (e ResourceType) Valid() bool {
 		ResourceTypeUserSecret,
 		ResourceTypeAiProvider,
 		ResourceTypeAiProviderKey,
-		ResourceTypeGroupAiBudget:
+		ResourceTypeGroupAiBudget,
+		ResourceTypeUserSkill:
 		return true
 	}
 	return false
@@ -3432,6 +3449,7 @@ func AllResourceTypeValues() []ResourceType {
 		ResourceTypeAiProvider,
 		ResourceTypeAiProviderKey,
 		ResourceTypeGroupAiBudget,
+		ResourceTypeUserSkill,
 	}
 }
 
@@ -5725,6 +5743,16 @@ type UserSecret struct {
 	ValueKeyID  sql.NullString `db:"value_key_id" json:"value_key_id"`
 }
 
+type UserSkill struct {
+	ID          uuid.UUID `db:"id" json:"id"`
+	UserID      uuid.UUID `db:"user_id" json:"user_id"`
+	Name        string    `db:"name" json:"name"`
+	Description string    `db:"description" json:"description"`
+	Content     string    `db:"content" json:"content"`
+	CreatedAt   time.Time `db:"created_at" json:"created_at"`
+	UpdatedAt   time.Time `db:"updated_at" json:"updated_at"`
+}
+
 // Tracks the history of user status changes
 type UserStatusChange struct {
 	ID        uuid.UUID  `db:"id" json:"id"`