Add community guidance and review support for Business Central agents (#137)

* feat(community/agents): add AL agent quality guidance

- add 20 agent knowledge rules with good and bad AL samples
- clarify setup dialog shape, temporary persistence, permissions, profiles, instructions, capability registration, and interface wiring
- add the community-owned AL agents review skill
- make review fixture discovery layer-aware with custom, community, and Microsoft precedence
- document layer-aware evaluation behavior

* fix(community/agents): align setup and permission samples

- mark agent setup pages as non-extensible where required
- narrow the agent profile by hiding an unrelated sales-order field
- define a dedicated read-only permission set for the sales review agent
- assign AL-defined permission sets with system scope and the owning app ID
- clarify the permission scope guidance for default access controls

* Address agent review feedback

community/knowledge/agents/do-not-create-agents-in-install-upgrade-or-background.md

@@ -0,0 +1,26 @@
+---
+bc-version: [27..]
+domain: agents
+keywords: [agent-create, install, upgrade, job-queue, interactive-session, background]
+technologies: [al]
+countries: [w1]
+application-area: [all]
+---
+
+# Do not create agent instances from install, upgrade, or background sessions
+
+## Description
+
+`Agent.Create` requires an interactive user session. The platform blocks creation from install codeunits, upgrade codeunits, and background sessions (job queue, scheduled tasks). Packaging an agent in an app does not mean spinning up instances at install. Models still call `Create` from `OnInstallAppPerCompany` to activate the agent.
+
+## Best Practice
+
+Create instances from a setup page, a wizard, or another UI-driven path after the user is in a client session. Apply instructions and `Activate` there. For existing companies after an upgrade, document that an admin must open setup; do not create from the upgrade codeunit.
+
+See sample: `do-not-create-agents-in-install-upgrade-or-background.good.al`.
+
+## Anti Pattern
+
+`Agent.Create` inside `OnInstallAppPerCompany`, `OnUpgradePerCompany`, or a job-queue codeunit. The call fails at runtime even if it compiles. Detection signal: `Agent.Create` in `Subtype = Install`, `Subtype = Upgrade`, or a non-UI session.
+
+See sample: `do-not-create-agents-in-install-upgrade-or-background.bad.al`.