Fail closed when hint segment create is not a YAML boolean

[jmjava]

Problem

yaml-generate inserts segments.all ids from hints/*.md when docgen.segment.create is truthy. Quoted create: "false" is a non-empty string, so it still declared the segment. A list stem was str()'d into segment_names; a list id failed the \d{2} check and was skipped as if the hint were prose-only.

YAML create: false already skipped. Integer id: 5 still pads to "05".

Change

parse_hint_segment_declaration requires:

• present create to be a YAML boolean
• stem to be a YAML string
• id to be a YAML string or integer (not bool/list)

Milestone: milestones/hint-segment-create-bool.md

Tests

• create: "false" raises
• list stem / id raise
• existing create: false skip and integer id: 5 pad tests remain