feat(ai): Enhance Perplexity research calls & fix docs examples

Improves the quality and relevance of research-backed AI operations:
- Tweaks Perplexity AI calls to use max input tokens (8700), temperature 0.1, high context size, and day-fresh search recency.
- Adds a system prompt to guide Perplexity research output.

Docs:
- Updates CLI examples in taskmaster.mdc to use ANSI-C quoting ($'...') for multi-line prompts, ensuring they work correctly in bash/zsh.

.changeset/tricky-papayas-hang.md

@@ -0,0 +1,9 @@
+---
+'task-master-ai': patch
+---
+- Tweaks Perplexity AI calls for research mode to max out input tokens and get day-fresh information
+    - Forces temp at 0.1 for highly deterministic output, no variations
+    - Adds a system prompt to further improve the output
+    - Correctly uses the maximum input tokens (8,719, used 8,700) for perplexity
+    - Specificies to use a high degree of research across the web
+    - Specifies to use information that is as fresh as today; this support stuff like capturing brand new announcements like new GPT models and being able to query for those in research. 🔥