docs: old product name F∆I Platform -> Ch∆In + contact chain@flemming.ai

The old 'F∆I Platform' product name and platform@flemming.ai contact
survived in docs/NOTICE/descriptions/help text; the product is Ch∆In and
the contact is chain@flemming.ai. Generic 'cross-platform/platform-native'
left untouched.

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

tools/install-hooks.sh

@@ -1,5 +1,5 @@
 #!/usr/bin/env bash
-# F∆I Platform — one-time hook activation for this clone.
+# Ch∆In — one-time hook activation for this clone.
 # Points git at the versioned `.githooks/` directory so pre-commit and
 # commit-msg checks run on every commit (including amends and rebases).
 #

tools/security/check-staged.sh

@@ -1,5 +1,5 @@
 #!/usr/bin/env bash
-# F∆I Platform — staged-content security check.
+# Ch∆In — staged-content security check.
 # Runs from .githooks/pre-commit, .githooks/commit-msg, and Forgejo CI.
 #
 # Modes:

tools/security/test-check-staged.sh

@@ -1,5 +1,5 @@
 #!/usr/bin/env bash
-# F∆I Platform — smoke tests for `tools/security/check-staged.sh`.
+# Ch∆In — smoke tests for `tools/security/check-staged.sh`.
 #
 # Spins up an isolated tempdir per scenario, stages a tripwire,
 # and asserts the security script either passes or fails with the