[Interactive Graph] Absolute value graph description polish.

[catandthemachines]

Summary:

Updating the Absolute value graph descriptions so the screen reader copy matches the Absolute outline doc, enriching the description with the visual detail that's essential for all learners:

• Which direction the graph opens (upward / downward).
• The vertex location (or "the origin" when it sits at 0, 0).
• The x- and y-intercepts.
• The slope of the arms.

Follows the same pattern as the exponential (#3786), logarithm (#3798), and vector (#3799) description polish.

Issue: LEMS-4286

Test plan:

Run pnpm storybook and open Widgets → Interactive Graph → Absolute value. These are screen-reader strings, so verify with a screen reader or by inspecting the element aria-labels / aria-describedby text. Check:

1. Graph description — announces the direction the graph opens, the vertex location, the intercepts, and the slope, e.g. "The graph opens downward. Vertex is at 0 comma 2. The X-intercepts are at -1 comma 0 and 1 comma 0. The Y-intercept is at 0 comma 2. The slope is -2." Drag the points to confirm it updates.
2. Vertex at the origin — the intercepts are omitted (they'd all be at the origin), e.g. "The graph opens upward. Vertex is at the origin. The slope is 1."
3. Vertex point — reads "Vertex point at X comma Y."
4. Arm point — reads "Point on arm at X comma Y." with a separate slope description (aria-describedby) of "The slope is S."
5. Interactive elements summary — "Absolute value graph with vertex point at …, arm point at …, and slope of …."
6. Live announcements — moving the vertex announces "Vertex point at X comma Y."; moving the arm point announces "Point on arm at X comma Y. The slope is S."

[github-actions]

npm Snapshot: Published

Good news!! We've packaged up the latest commit from this PR (ed6dd35) and published it to npm. You
can install it using the tag PR3800.

Example:

pnpm add @khanacademy/perseus@PR3800

If you are working in Khan Academy's frontend, you can run the below command.

./dev/tools/bump_perseus_version.ts -t PR3800

If you are working in Khan Academy's webapp, you can run the below command.

./dev/tools/bump_perseus_version.js -t PR3800

[github-actions]

Size Change: +668 B (+0.13%)

Total Size: 514 kB

📦 View Changed

Filename	Size	Change
packages/perseus/dist/es/index.js	204 kB	+352 B (+0.17%)
packages/perseus/dist/es/strings.js	8.91 kB	+316 B (+3.68%)

ℹ️ View Unchanged

Filename	Size
packages/kas/dist/es/index.js	20.6 kB
packages/keypad-context/dist/es/index.js	1 kB
packages/kmath/dist/es/index.js	6.32 kB
packages/math-input/dist/es/index.js	98.5 kB
packages/math-input/dist/es/strings.js	1.61 kB
packages/perseus-core/dist/es/index.item-splitting.js	12.3 kB
packages/perseus-core/dist/es/index.js	27.3 kB
packages/perseus-editor/dist/es/index.js	105 kB
packages/perseus-linter/dist/es/index.js	9.8 kB
packages/perseus-score/dist/es/index.js	10.2 kB
packages/perseus-utils/dist/es/index.js	403 B
packages/pure-markdown/dist/es/index.js	1.39 kB
packages/simple-markdown/dist/es/index.js	6.71 kB

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