Make plugin name validation regex-portable

[jonathanhefner]

Problem

The plugin manifest schema uses a negative lookahead to enforce name constraints. Although the expression is valid ECMA-262, lookaround is outside the portable subset recommended by JSON Schema and cannot be compiled by RE2-based validators, such as those using Go regexp.

The full-string expression also relies on $ behavior that differs across regular-expression engines. In particular, engines that let $ match before a terminal newline can accept a name that §5.5 rejects.

Resolution

Replace the lookahead with two ordinary JSON Schema assertions:

• pattern requires the name to begin with a lowercase ASCII alphanumeric character.
• not.pattern rejects disallowed characters, punctuation at the end, --, and ...

Both pattern and not are standard Draft 2020-12 keywords, so the correction introduces no custom validation mechanism.

This keeps all patterns within the broadly portable subset and preserves the constraints defined by §5.5. Explicitly rejecting disallowed characters also makes terminal-line-break behavior consistent across engines.

The correction applies to the 1.1.0 working draft. The published 1.0.0 schema retains its canonical contents.

Validation

An AI agent:

• Compiled schemas/1.1.0/plugin.schema.json as Draft 2020-12 with Ajv.
• Compared the replacement assertions with the §5.5 predicate across 137,257 generated names with no mismatches.
• Checked mixed punctuation, repeated punctuation, invalid characters, punctuation endpoints, terminal line breaks, and 64/65-character boundaries.

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Closes #76.