Add hover support linking eslint-disable directives to rule documentation

[Copilot]

Hovering an eslint-disable* / eslint-enable directive comment now surfaces a link to the referenced rule's documentation, the same way the diagnostic underline does today.

// eslint-disable-next-line security/detect-non-literal-fs-filename -- harmless here
await fs.writeFile(outputPath, data);
//                 ^ hovering the rule id now shows a link to its docs page

Changes

• Directive parser (server/src/eslint.ts) — New DirectiveComments namespace parses a line into the directive keyword plus each referenced rule id with character ranges. Handles eslint-disable, eslint-disable-line, eslint-disable-next-line, eslint-enable; scoped/plugin rule ids; comma-separated lists; the -- description suffix; and block-comment terminators. Exposes findRuleAt (exclusive-end token lookup) and contains (region membership).
• Hover handler (server/src/eslintServer.ts) — New connection.onHover returns Markdown links from RuleMetaData.getUrl for the rule under the cursor, or all rules when hovering the keyword. Advertises hoverProvider capability. Gated to validated documents and to directives that actually sit inside a comment.
• Tests / docs — Unit tests for the parser; CHANGELOG entry.

Notes

• No client changes required: the existing document selector routes hover requests, and the server returns null for non-synced/non-validated documents.
• Links reuse the rule metadata captured during linting (consistent with the existing "Show documentation" code action), so a link is available once a rule has reported — typically the point at which the disable directive was added. Rules with no captured URL yield no hover rather than a dead link.