refactor: split Nip34WritePolicy into focused sub-policies

Split the ~900 line Nip34WritePolicy into focused sub-policies for improved
testability and maintainability:

- AnnouncementPolicy - Repository announcement validation
- StatePolicy - State event validation + ref alignment
- PrEventPolicy - PR/PR Update validation
- RelatedEventPolicy - Forward/backward reference checking

The main Nip34WritePolicy now delegates to these sub-policies via a shared
PolicyContext that provides domain, database, and git_data_path.

Also updates:
- README.md: Accurate project structure reflecting actual implementation
- docs/learnings: Marks this technical debt item as complete

1 files changed, 41 insertions, 0 deletions

diff --git a/src/nostr/policy/mod.rs b/src/nostr/policy/mod.rs
new file mode 100644
index 0000000..6d67394
--- /dev/null
+++ b/src/nostr/policy/mod.rs
@@ -0,0 +1,41 @@
+/// Policy module for NIP-34 write policies
+///
+/// This module splits the large Nip34WritePolicy into focused sub-policies:
+/// - `AnnouncementPolicy` - Repository announcement validation
+/// - `StatePolicy` - State event validation + ref alignment
+/// - `PrEventPolicy` - PR/PR Update validation
+/// - `RelatedEventPolicy` - Forward/backward reference checking
+
+mod announcement;
+mod pr_event;
+mod related;
+mod state;
+
+pub use announcement::{AnnouncementPolicy, AnnouncementResult};
+pub use pr_event::PrEventPolicy;
+pub use related::{ReferenceResult, RelatedEventPolicy};
+pub use state::{AlignmentResult, StatePolicy, StateResult};
+
+use super::SharedDatabase;
+
+/// Shared context for all sub-policies
+#[derive(Clone)]
+pub struct PolicyContext {
+    pub domain: String,
+    pub database: SharedDatabase,
+    pub git_data_path: std::path::PathBuf,
+}
+
+impl PolicyContext {
+    pub fn new(
+        domain: impl Into<String>,
+        database: SharedDatabase,
+        git_data_path: impl Into<std::path::PathBuf>,
+    ) -> Self {
+        Self {
+            domain: domain.into(),
+            database,
+            git_data_path: git_data_path.into(),
+        }
+    }
+}
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