[MWPW-205938] Add contextual accessible names for Share, Favorite, an…

[rea16068]

Fixes MWPW-205938: four session-page controls were missing contextual accessible names per the Stark/Figma annotations, making them indistinguishable to screen-reader users ("Show more", "Show more" repeated with no context).

Changes

1. Share button: accessible name is now Share ${sessionTitle}, falling back to bare "Share" (no trailing space) if no title.
2. Favorite button: accessible name is now Favorite ${sessionTitle} (dropped "this session"), set once at construction — does NOT change when toggled, since aria-pressed already conveys on/off state.
3. Four show-more toggles (speakers, featured products, session resources, description): added a visually-hidden .sr-only span alongside the existing aria-hidden visible label, so screen readers hear "Show more products" / "Show more speakers" / etc., while the visible text stays "Show more"/"Show less" as designed.

Both title-resolving controls use the same logic as the page H1: getMetadata('title') || getMetadata('en-title') — intentionally NOT the event-title metadata used elsewhere for toast copy.

Resolves: MWPW-205938

Built on top of #312 (MWPW-205937)

This PR is based on MWPW-205937-analytics-tagging rather than dev, since it touches the same four toggle files and needs the explicit daa-ll attributes already in place. The sr-only span's textContent change does NOT affect daa-ll — verified both are updated independently in each click handler, and existing daa-ll assertions still pass unchanged.

Out of scope

• Nothing under event-libs/v1/c2/blocks/sessions-guide/ — it already has its own working accessible names.
• Playlist/video-player controls — no such block exists in event-libs.

Test plan

• Unit tests: 134/134 passed on the affected specs
• JS lint: clean
• CSS lint: clean (npx stylelint 'event-libs/v1/c2/blocks/event-*/**/*.css')
• Extended 6 existing spec files per the ticket, including re-verifying MWPW-205937's daa-ll assertions still pass with the sr-only span present.

Merge note: this PR should be merged (or rebased onto dev) after #312 merges first.

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Commits

• 14889df ✅ (latest)