feat: implement prefix matching experiment (#2947)

[krish-mittal1]

Description

Closes #2947

This PR introduces an experimental feature for Shortest Unique Prefix Matching (segment-wise abbreviation matching) behind the PREFIX_MATCHING experiment flag (TASK_X_PREFIX_MATCHING=1 or .taskrc.yml).

Summary of Changes:

• Segment Prefix Matching: Checks input against task names and aliases segment-by-segment separated by : (e.g. task a:o:e or task api:o matches api:openapi:export).
• Conflict Handling: Halts execution and returns a TaskNameConflictError listing all candidate matches when an input prefix is ambiguous.
• Precedence: Ensures direct matches, alias matches, and wildcard matches always take precedence over prefix matching.
• Internal Task Protection: Excludes internal tasks from prefix matching candidates.
• Documentation & Schema: Added experiment documentation (website/src/next/docs/experiments/prefix-matching.md) and updated .taskrc.yml JSON schema.
• Testing: Added comprehensive unit and integration tests covering single-segment, multi-segment, alias prefixes, ambiguity, and precedence rules.

Checklist

• I have read and followed the Contribution Guide.
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• I fully understand the changes and have hand-written the description (No AI) of this pull request.