fix(rune): replay queued displays once

[11suixing11]

Summary

• queue rune display messages until the Rune tab sends its first request
• replay the queued backlog exactly once when the tab requests it
• keep later displays streaming live after the request has established the tab subscriber
• add a regression test using the real Conductor Channel pair for the pre-request display flow

Reproduction covered

The new test fails on the previous implementation with render modes anaglyph, normal, anaglyph instead of the expected normal, anaglyph.

Tests

• git diff --check
• corepack yarn workspace @sourceacademy/bundle-rune test
• corepack yarn workspace @sourceacademy/bundle-rune tsc
• corepack yarn workspace @sourceacademy/bundle-rune lint
• corepack yarn workspace @sourceacademy/bundle-rune build

Addresses #823.

[gemini-code-assist]

Caution

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