Implement identical-links-same-context rule (fd3a94)

## ACT Rule
- **ACT Rule ID:** [fd3a94](https://www.w3.org/WAI/standards-guidelines/act/rules/fd3a94/)
- **Rule Name:** Links with identical accessible names and same context serve equivalent purpose
- **WCAG SC:** 2.4.4 Link Purpose (In Context) (Level A)

## What it checks
This rule checks that links with identical accessible names that are in the same context point to equivalent resources.

## Feasibility
**DOM-only feasible.** Involves finding links with the same accessible name, grouping by context, and checking if href attributes point to equivalent resources.

## Notes
- Related to issue #350 (ACT rules triage)
- The existing `identical-links-same-purpose` scanner rule (mapped to ACT rule b20e66) covers links regardless of context; this is the same-context variant
- May be able to extend the existing rule implementation

Start by locating the existing `identical-links-same-purpose` scanner rule and its implementation, then compare it with ACT rule fd3a94 and the related issue #350. The change is complete when links with identical accessible names are grouped by context and their hrefs are checked for equivalent resources, while preserving the existing rule's behavior.

Written by the indexing model from the issue text.