chore: rename packages/ to crates/

Move all 29 workspace members from packages/<name>/ to crates/<name>/.
Updates: workspace Cargo.toml (members + path deps), justfile, root
CLAUDE.md, scripts/build/CARGO_INSTALL.md, docs/architecture/crates.md
(renamed from packages.md), structural references in docs/architecture
and docs/configuration, per-crate CLAUDE.md self-references. Historical
plans, reports, and building/ docs are left untouched.

No behavior change; just check-all stays green and fermata tests pass.

src/core/decision.rs

@@ -0,0 +1,30 @@
+use serde::{Deserialize, Serialize};
+use std::path::PathBuf;
+
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+pub struct Rule {
+    /// Source file the rule came from (e.g. `/proj/.botignore`).
+    pub source: PathBuf,
+    /// Pattern text as it appeared in the source.
+    pub pattern: String,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+pub struct Reason {
+    pub message: String,
+    pub rule: Option<Rule>,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(tag = "kind", rename_all = "lowercase")]
+pub enum Decision {
+    Allow,
+    Ask(Reason),
+    Deny(Reason),
+}
+
+impl Decision {
+    pub fn is_blocking(&self) -> bool {
+        matches!(self, Decision::Deny(_))
+    }
+}