Re-accept hyphen-delimited hook sections with deprecation warning

[jensens]

Summary

5.3.1 anchored hook section matching strictly on :, which broke downstream hooks (notably mxmake) that emit [namespace-section] sections — those sections were reclassified as packages and tripped ValueError("Section X has no URL set!") on the first mxdev run after upgrade.

This PR re-accepts the historical - delimiter for backward compatibility, logs a one-time deprecation warning per offending section, and normalizes hook namespaces that bake a trailing - into the namespace string (e.g. namespace = "mxmake-").

Recognized hook section forms:

Form	Status
[namespace]	exact match, canonical
[namespace:subsection]	colon delimiter, canonical
[namespace-subsection]	hyphen delimiter, deprecated, logs warning

The original #88 bug stays fixed: a package whose name merely starts with the namespace without a delimiter (e.g. uvst.addon for namespace "uv") is still a package, not a hook section.

Why

mxmake declares namespace = "mxmake-" and emits [mxmake-env], [mxmake-<template>] sections in every generated mx.ini. Under 5.3.1 these are misclassified as packages → hard-fail. Rather than force every downstream user to regenerate their mx.ini in lockstep with 5.3.1, accept the old form with a deprecation pointing users at the new syntax.

A separate issue will be filed against mxstack/mxmake to plan the migration to colon syntax.

Test plan

• test_hook_section_with_hyphen_delimiter_is_supported_but_deprecated — [mxmake-env] is a hook section AND a deprecation warning is logged
• test_legacy_namespace_with_trailing_hyphen_is_normalized — namespace = "mxmake-" works for both [mxmake-env] and [mxmake:files]
• test_hyphen_prefix_without_delimiter_is_still_a_package — uvst.addon regression from Fix hook namespace swallowing packages with a matching name prefix #88 still holds
• test_hook_section_with_namespace_delimiter_belongs_to_hook — colon form still works
• Full suite: 215 passed, 4 skipped
• tox -e lint passes