Make README finance-focused; consolidate finance programs into finance/

Reorder the Financial Software section to lead with Escrow (the
recommended first finance program), then Order Book based Exchange,
then AMM based Exchange, followed by Token Fundraiser and Vault
Strategy. Rewrite descriptions to be approachable to readers learning
Solana and finance at the same time.

Move all finance programs into a new finance/ directory:
- finance/escrow (from tokens/)
- finance/order-book (from defi/)
- finance/token-swap (from tokens/)
- finance/token-fundraiser (from tokens/)
- finance/vault-strategy (from defi/)
defi/ is removed. Pyth is an oracle-reading single-concept example
rather than a finance program, so move oracles/pyth to basics/pyth
and list it under the renamed 'Single concept examples' section
(formerly 'Basics'); oracles/ is removed.

Update workspace members in Cargo.toml, ignored paths in
.github/.ghaignore, and order-book internal path references.

https://claude.ai/code/session_01CfCCGCXne6eViGamZwy7ot

Author: claude

.github/.ghaignore

@@ -12,10 +12,10 @@ tokens/transfer-tokens/native
 tokens/token-minter/native
 tokens/create-token/native
 
-tokens/token-swap/anchor
+finance/token-swap/anchor
 
 # not building
-oracles/pyth/anchor
+basics/pyth/anchor
 
 # not building
 compression/cutils/anchor
@@ -25,7 +25,7 @@ compression/cnft-burn/anchor
 
 # test failing
 # https://github.com/solana-developers/helpers/issues/40
-tokens/escrow/anchor
+finance/escrow/anchor
 
 # not live
 tokens/token-extensions/group/anchor
@@ -65,9 +65,9 @@ basics/realloc/steel
 basics/rent/steel
 basics/transfer-sol/steel
 
-tokens/escrow/steel
+finance/escrow/steel
 
 tokens/pda-mint-authority/steel
 tokens/token-minter/steel
-tokens/token-swap/steel
+finance/token-swap/steel
 tokens/transfer-tokens/steel

Cargo.toml

@@ -48,9 +48,9 @@ members = [
     "basics/transfer-sol/anchor/programs/*",
     "basics/transfer-sol/asm",
 
-    # defi
-    "defi/vault-strategy/anchor/programs/vault-strategy",
-    "defi/vault-strategy/anchor/programs/mock-swap-router",
+    # finance
+    "finance/vault-strategy/anchor/programs/vault-strategy",
+    "finance/vault-strategy/anchor/programs/mock-swap-router",
 
     # tokens
     "tokens/token-extensions/mint-close-authority/native/program",