Fix flag tag_expr to follow same format as config and allow misc characters

[Copilot]

What's Changed

Tag expressions via --tags-expr flag were too restrictive compared to config file tag definitions. Now allows special characters (hyphens, dots, etc.) matching config behavior.

Technical Description

• Updated tag expression lexer to accept any non-reserved characters in tags
• Reserved chars remain: (, ), !, &, |, and whitespace
• Added documentation for valid tag characters in docs/filtering-projects.md
• Added changelog entry for 0.31.2

Example: Tags like v1.0, my-tag, @scope/package now work in expressions:

mani run build --tags-expr 'frontend-v2 && !legacy.old'

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