Installer prerequisites: REQ-D through REQ-G

REQ-D: restore waitress and tzdata to requirements.in. They existed ONLY in the
generated requirements.txt (hand-added in bf9e60e), so the next
`uv pip compile` would have silently removed the WSGI server and the IANA
timezone database from every Windows install.

REQ-E: split production and development requirements. requirements.txt was
installing pytest, pytest-cov, pytest-flask, coverage, iniconfig and pluggy onto
production servers. Verified on a real Windows Server box before this change.
CI, scripts/test-external-plugin.sh and the dev docs now use requirements-dev.txt.

REQ-F: standardise on Python 3.14. The repo declared four different versions
(Dockerfile 3.12, DEPLOY-WINDOWS-IIS 3.12, INSTALL-WINDOWS-IIS 3.13, CI 3.13,
plus README, web.config and PLUGIN-EXTERNAL-REPO). 3.14 is in active bugfix
support until ~Apr 2027 and supported to Oct 2030; 3.13 entered security-only in
Apr 2026. All four compiled dependencies publish win_amd64 wheels for 3.14
(cryptography via an abi3 wheel), verified by building an offline wheelhouse and
installing it on Windows Server 2025.

REQ-G: state MySQL 8.0 as the standard for new installs; 5.7+/5.6 remain
supported on an existing server.

Lockfiles regenerated with uv pip compile. Production deps 44 -> 38.

requirements.in

@@ -24,10 +24,14 @@ requests>=2.31
 # Security
 werkzeug>=3.0
 
+# Windows/IIS runtime
+# waitress is the WSGI server IIS launches via HttpPlatformHandler.
+# tzdata ships the IANA timezone database, which Windows does not provide;
+# without it the notifications plugin fails on zoneinfo lookups.
+# Both were previously hand-added to requirements.txt only, so a recompile
+# would have silently dropped them from every Windows install.
+waitress>=3.0
+tzdata
+
 # Validation
 email-validator>=2.0
-
-# Testing
-pytest>=7.0
-pytest-flask>=1.2
-pytest-cov>=4.0