chore: track .icp/data/mappings via .gitkeep and clarify .gitignore

bitcoin-starter/.gitignore

@@ -13,5 +13,7 @@
 # rust
 target/
 
-# icp-cli
+# icp-cli local cache (safe to delete, rebuilt on next build/deploy)
 .icp/cache/
+# Do NOT ignore .icp/data/ — it stores mainnet canister ID mappings.
+# See: https://github.com/dfinity/icp-cli/blob/main/docs/concepts/project-model.md#whats-safe-to-delete

hello-world/.gitignore

@@ -10,5 +10,7 @@
 # environment variables
 .env
 
-# icp-cli
+# icp-cli local cache (safe to delete, rebuilt on next build/deploy)
 .icp/cache/
+# Do NOT ignore .icp/data/ — it stores mainnet canister ID mappings.
+# See: https://github.com/dfinity/icp-cli/blob/main/docs/concepts/project-model.md#whats-safe-to-delete

motoko/.gitignore

@@ -14,5 +14,7 @@
 .mops
 *.wasm
 
-# icp-cli
+# icp-cli local cache (safe to delete, rebuilt on next build/deploy)
 .icp/cache/
+# Do NOT ignore .icp/data/ — it stores mainnet canister ID mappings.
+# See: https://github.com/dfinity/icp-cli/blob/main/docs/concepts/project-model.md#whats-safe-to-delete

proxy/.gitignore

@@ -0,0 +1,4 @@
+# icp-cli local cache (safe to delete, rebuilt on next build/deploy)
+.icp/cache/
+# Do NOT ignore .icp/data/ — it stores mainnet canister ID mappings.
+# See: https://github.com/dfinity/icp-cli/blob/main/docs/concepts/project-model.md#whats-safe-to-delete

rust/.gitignore

@@ -13,5 +13,7 @@
 # rust
 target/
 
-# ingore the icp-cli cache
+# icp-cli local cache (safe to delete, rebuilt on next build/deploy)
 .icp/cache/
+# Do NOT ignore .icp/data/ — it stores mainnet canister ID mappings.
+# See: https://github.com/dfinity/icp-cli/blob/main/docs/concepts/project-model.md#whats-safe-to-delete

static-website/.gitignore

@@ -22,3 +22,8 @@ dist-ssr
 *.njsproj
 *.sln
 *.sw?
+
+# icp-cli local cache (safe to delete, rebuilt on next build/deploy)
+.icp/cache/
+# Do NOT ignore .icp/data/ — it stores mainnet canister ID mappings.
+# See: https://github.com/dfinity/icp-cli/blob/main/docs/concepts/project-model.md#whats-safe-to-delete