fix(pdo-fbird): make split package self-contained

[satwareAG-ironMike]

Problem

pie install satwareag/pdo-fbird fails with:

fatal error: ../firebird_utils.h: No such file or directory

The pdo-fbird PIE package (split to satwareAG/pdo-fbird repo) references parent headers (../firebird_utils.h, ../php_firebird.h, etc.) that don't exist in the split repo.

Fix

Copy 5 shared headers + VERSION.txt into pdo_fbird/ directory so the split package is self-contained:

File	Size	Purpose
firebird_utils.h	54KB	Utility function declarations
php_fbird_includes.h	23KB	Core includes (types, macros, constants)
php_firebird.h	6KB	Extension registration
fbird_classes.h	4KB	OOP class declarations
fbird_service_types.h	1KB	Service manager types
VERSION.txt	7B	Version string (for config.m4)

Then changed all #include "../xxx.h" to #include "xxx.h" (local references).

Also rewrote config.m4:

• Removed PHP_ADD_INCLUDE([$srcdir/..])
• Changed $srcdir/../VERSION.txt to $srcdir/VERSION.txt

Verification

Split build (simulated PIE install)

cd /tmp/pdo-fbird-split/  # isolated copy with only pdo_fbird/ + headers
phpize && ./configure --with-pdo-fbird --with-firebird=/usr && make
# => Build complete. modules/pdo_fbird.so created

In-tree build (main repo)

phpize && ./configure --with-firebird=/usr && make
# => Both firebird.so and pdo_fbird.so build successfully

No ../ references remain

grep -rn '\.\./' pdo_fbird/config.m4 pdo_fbird/config.w32 pdo_fbird/*.c pdo_fbird/*.h
# (none)

Split workflow

No changes needed to split-stubs.yml. The danharrin/monorepo-split-github-action does a subtree split of pdo_fbird/, which now includes all the shared headers.

After merge

1. Tag v13.0.3 (version bump)
2. split-stubs.yml pushes the fixed pdo_fbird/ to satwareAG/pdo-fbird
3. Packagist picks up the new tag
4. pie install satwareag/pdo-fbird will work

Relates: #485