fix(migrations): restore 095_provider_node_custom_headers (deleted again by #3371 squash)

Same issue as after #3365: git rm in the contributor cleanup commit
was included in the squash, deleting this migration from release.
Permanent fix needed: use 'git checkout origin/release -- <file>'
instead of 'git rm' when cleaning up duplicate files in contributor branches.

src/lib/db/migrations/095_provider_node_custom_headers.sql

@@ -0,0 +1,5 @@
+-- Add custom_headers_json column to provider_nodes
+-- Stores JSON object of custom HTTP headers to send with requests to this provider
+-- NULL = no custom headers (backward compatible)
+-- Column uses _json suffix so rowToCamel auto-parses it
+ALTER TABLE provider_nodes ADD COLUMN custom_headers_json TEXT;