v0.1.4: PGXN Distribution

v0.1.4: PGXN Distribution

v0.1.4 adds PGXN distribution metadata and a top-level Makefile for
source-based installation via PGXN. Existing v0.1.3 users should not
need to change their SQL or application code.

Highlights

• Added PGXN META.json distribution metadata at the repository root.
• Added a PGXN-compatible top-level Makefile that delegates to cargo pgrx.
• Added PGXN and manual source installation documentation to README.md,
  README_zh.md, and the user guide.
• Documented PG_CONFIG targeting and missing PostgreSQL header
  troubleshooting for source installs.
• Prepared pgGraph for source-based PGXN release.

Validation

Run the PGXN metadata validation (cargo install pgxn_meta --locked):

pgxn_meta

Run the PGXN-style build flow:

make
make installcheck